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Showing posts with label biological realism. Show all posts
Showing posts with label biological realism. Show all posts

Monday, July 26, 2010

Real Sex vs. the Contraceptive Mentality (Part 4 & Conclusion)

[Continued from Part 1, Part 2, and Part 3]

NFP and the Contraceptive Mentality

In concluding this series, I'd like to address the question which originally set me on on this overly extended journey: Is it possible for users of Natural Family Planning to have a "contraceptive mentality" and if so what does that mean in the context of NFP?

I've described the contraceptive mentality as: The idea that having sex and reproducing are two activities with no necessary connection, that having sex in no way suggests a desire or willingness to have children with the person you are having sex with.

At root, I think that NFP is formulated in such a way as to be in direct opposition to the contraceptive mentality. According to an understanding of sexuality rooted in human instinct and biological reality, the way to avoid conceiving children is to not have sex. This is also the means of avoiding conception which is considered acceptable by the Church in the context of its understanding of the moral nature of sexuality. NFP is considered morally acceptable by the Church for the reason that it consists of avoiding pregnancy by not having sex, with the modern refinement of allowing the married couple to understand with a certain degree of confidence when it is that they need to avoid having sex in order to avoid conception. Rather than abstaining all the time in order to avoid pregnancy, the couple can abstain for between a quarter and half out of the woman's cycle, and achieve the same result with relative certainty.

For us as human persons, this requires a degree of self mastery over our natural instincts. The modern NFP-using married couple finds itself in a situation (well housed and fed by historical standards, healthy, and lying in bed with a member of the opposite sex with whom one would certainly not object to having conjugal relations) which would seem to scream: Have sex! Reproduce! But for various prudent reasons arrived at by human reason, they may well consider it important at a given time to overcome that instinct and abstain for a portion out of each month in order to avoid having children for a time.

However, while this use of periodic abstinence to avoid pregnancy does not necessarily involve the contraceptive mentality, indeed emphasizes quite the opposite, I think that as NFP-using couples we do find ourselves subject to the temptations of the wider culture in this regard.

The assumption which has, over the last 80+ years since the use of artificial birth control became widespread, become so basic to our culture as to be completely unspoken and unconscious, even among those of us who see ourselves as standing in opposition to it, is that a happily married husband and wife will have a "good sex life" consisting of regular marital relations, sometimes passionate or creative, sometimes comfortable and familiar, which expresses the couples love and affection for one another. Even for those of us who see fertility as a part of our marriage equal to and related to conjugal bliss, it's nearly impossible to shake the feeling of, "We're married; we should be able to do this."

Some NFP guides try to soften and direct this frustration: During the fertile part of the cycle, if you are delaying pregnancy, is a great time for date nights and cuddling and other non-sexual expressions of affection.

The message seems to be that one should somehow be able to channel all of one's desire for sex into the non-fertile periods of the cycle. You, as an NFP user can have sex whenever you want, if only you can first have the first have the self control to only want it when you can have it! And you should be able to do this, because marriage isn't just about sex. Just be organized enough to schedule the non-sexual parts of your marital relationship for the fertile parts of the wife's cycle.

I think this overly optimistic view of NFP misses a basic understanding of human nature which we ignore to our own confusion and frustration: We are as creatures designed to "want" to reproduce a good deal more than we as thinking human beings desire to, and going against our instincts in this realm requires a degree of self denial which is often experienced as frustration or unhappiness. We are unlikely to feel entirely satisfied while practicing NFP because practicing it means denying our instincts.

This is particularly hard for us in the modern world because the understanding of sex which existed before the 20th century is remote and nearly irrecoverable for us -- the understanding which saw it as something of a double-edged sword, intensely pleasurable but at the same time as potentially high in cost. If the relationships of prior centuries often seem to our modern eyes a bit distant or dour, it is in part because it is impossible for us to recover the real sense of potential cost which applied to sexual intercourse -- both because pregnancy is less risky now and because even for those who have never in their lives used contraception the idea that "we should be able to have sex" is inescapable.

I don't think that this is in any way a strike against NFP. Certainly, it makes the spacing of children easier upon a couple than not having the ability to read the signs of fertility, and I think that the reduced sense of risk or fear surrounding sex is indeed a good thing for marital relationships. However, we must at the same time understand that in seeking to apply prudence to our reproduction, and do so without use of artificial means which separate sex and reproduction, we necessarily will have to exert a degree of self control which will result in some degree of difficulty and frustration. If we deceive ourselves that such things can be achieved without difficulty, we set ourselves up for nothing but frustration and disappointment.

For those of us who reject artificial contraception, not getting pregnant requires not having sex, and not having sex means denying one's natural desires, which, as any dieter can tell you, requires self denial which is not always pleasant.

Tuesday, June 29, 2010

Real Sex vs. the Contraceptive Mentality (Part 3)

[Continued from Part 1 and Part 2]

Enter Artificial Birth Control

In Part 2, I discussed the sense in which marriage customs and sexual morality can be seen as an adaptive response to controlling childbearing. I'd like now to turn to the question of artificial birth control.

In my first job out of college, a small chemical distribution company, I sat next to the customer service group, and thus found myself overhearing a lot of middle-aged "girl talk". One anecdote I particularly remember was recounted by a woman who'd married in the late sixties. She told about how when she and her husband were still engaged, she'd gone with her mother to a wedding, and her mother had taken occasion to whisper to her that it was generally known that the bride had "had to get married."

"I'm just so glad you're a good girl and you'll never need to get married quickly like that, my mother told me," she said. "Of course, what she didn't know is that I'd been on the pill for the last three years."

I think this does a good job of underlining a massive shift in social structure and morality which the advent of plentiful and efficient birth control allowed. The adherance to social and moral norms ("being a good girl" as the mother put it), which had previously been essential for avoiding the bearing of children out of wedlock or a hasty marriage to the father of an impending child, was now rended unnecessary by The Pill. Artificial birth control is certainly not 100% effective, but it is effective enough to allow people to separate sex and reproduction in their minds. Having sex with some given person or at some given time becomes one choice, having a baby with some given person or at some given time becomes a totally separate and unrelated choice.

This, I would argue, is the "contraceptive mentality" in its most basic form: the idea that having sex and reproducing are two activities with no necessary connection, that having sex in no way suggests a desire or willingess to have children with the person you are having sex with.

From a societal point of view, I think this puts us into a state of clear and major change. Whereas there used to be very clear biological and societal reasons to strongly pressure people not to engage in sex outside of marriage (primarily women -- there was always the double standard resulting from the fact that it is women who become pregnant) in addition to the moral reasons which we as Christians recognize, these practical and secular reasons for avoiding sex outside of stable relationships have been reduced to half-hearted (and unpersuasive) suggestions like: Wait until you are emotionally ready.

Who, after all, at such a moment is really sitting around thinking, "Oh, but perhaps I'm not emotionally ready."

Thus, when its full implications are considered, the contraceptive mentality removes virtually all of the practical reasons for seeking permanence and exclusivity in sexual relationships. And, indeed, the loss of these is pretty much what we see around us.

However, this renders us very confused creatures. As biological creatures, we still have the physical pleasures and instinctual emotional ties associated with sex which developed because of its reproductive function. And yet most of us do not think of sex as being reproductive. The fact that natural incentive and natural effects have been so totally disengaged must have a major effect on us -- and the fact that sex is something both so attractive and so essential to the relationships which are the building blocks and perpetuators of society means that the imbalance resulting from this de-coupling of incentive and effect will reverberate throughout society in major ways.

[to be continued: Part 4]

Tuesday, June 22, 2010

Real Sex vs. the Contraceptive Mentality (Part 2)

[Continued from Part 1]

Restraint, Relationships and Planning Parenthood

When I say that we "naturally want to avoid having children" at certain times, I would imagine that the image that comes immediately to mind is of birth control, abortion or infanticide, and most traditional societies have seen these in some form or other. However, I'd like to turn our attention to something so basic and so prevalent that we don't think about it much.

From an anthropological point of view, the entire structure of our romantic and family relationships serves as a way to control childbearing, limitting it to situations in which offspring can be supported. Consider: Requiring that young women remain virgins until marriage ensured that children will not be born without a provider. Nor was the decision to marry, when it came, a strictly individual affair. Marriage was negotiated and approved by the wider families, because the families were in effect committing to help support the new family unit being created. Many cultures also required the husband's family to pay a "bride price", not simpy as compensation for the lost contribution of the daughter to her own family, but as proof that the husband was of sufficient means to start a family.

Once in place, this set of cultural mores and laws provided an easy way to adjust to want or plenty: In good times, people married young, in bad they married late and some did not marry at all. Within a marriage, the strong cultural ideal of the faithful wife ensured that if husband and wife avoided intercourse to space children the husband would not find some other male getting his genes in on the sly, while the cultural rules surrounding legitimacy assured the wife that even if her husband was unfaithful during such a time, any children resulting would not supplant hers in terms of inheritance or prestige.

A dramatic example of the extent to which marriage age was used to manage fertility can be seen in Wrigley's Population History of England, which makes a strong case that the English population explosion in the mid eighteenth century through the early twentieth was a result of a decline of in the average age of first marriage for women from 26 to 23. (This, coming at the same time as increased life expectancy caused the population to grow dramatically, and triggered a round of Malthusian worrying by the cultural elites.)

With marriage choices as the primary means of regulating reproduction, the other key factor, in addition to marriageable age, was the number of people who never married. In Western Europe from the Middle Ages through the Industrial Revolution, 10-25% of women never married. In poorer countries such as Ireland, both late marriage and spinsterhood came into play with the result that as few as 30% of the women of childbearing age were married at any given time. (Comprehensive demographic data here. Example table of percentage of women of childbearing age married by country and decade available on page 21 of this paper.)

What we see when we view demographic history is that marriage (and chastity outside of marriage) is an adaptive trait which allows us as rational creatures to regulate our fertility. The fact that the signs of female fertility are hard to discern means that any sexual act with a woman of childbearing age may result in the creation of a child. And the set of moral and societal norms surrounding marriage provide us with a way to manage that fact responsibly in order to have children only when we believe we can support them. This evolutionary analysis actually leads to a definition of marriage which is startlingly similar to a traditional Christian understanding of marriage: In both cases one of the primary ends of marriage is to assure that children come into being only when others are prepared to love and care for them.

[to be continued: Part 3]

Wednesday, June 16, 2010

Real Sex vs. the Contraceptive Mentality (Part 1)

If you move in conservative Catholic circles much, you have doubtless heard the phrase "contraceptive mentality". Though used frequently and negatively, I think there is value in delving a bit more deeply into what we mean by the phrase. I was moved to write this in semi-response to an interesting post by Brett Salkeld a couple months back which sought to explore the bounds of what a "contraceptive mentality" is. Another good resource on the topic is this post at Catholic Culture on the contraceptive mentality.

While recognizing the dangers of trying to be too wide ranging in subject matter in the limited space of a blog post, my goal here is to set out answers to the following:
  • What is a "contraceptive mentality"?

  • How is a contraceptive mentality contrary to how humans are "meant" to function morally and sexually?

  • How, if at all, does NFP (natural family planning) relate to a contraceptive mentality?


I think it's easiest to think about the idea of a contraceptive mentality against the backdrop of how we function sexually as human creatures -- a term I use advisedly in that I want to emphasize our rootedness in a certain biological reality of being primates with certain biological systems and instincts, while at the same time not ignoring our rational, emotional and moral sensibilities in the sense that "human animal" strikes me as implying.

Uncertainty and Conception

One thing that sets us apart from most other higher primates is that humans have fairly even sexual drive all of the time. Or, at least, men have sexual drive pretty much all of the time. Women seem to have more variation in their level of interest, and indeed there is a fair amount of evidence that one driving (though unconscious) element of their drive is that they are more "in the mood" during the times of the month when they are fertile than when they are not. Another thing that sets us apart from most other higher primates is that a woman's fertility is not marked by unmistakable physical signs (change of color and swelling of the genital area, changes in smell, etc.) (Though Bonobos have often been compared to humans in regards to their relatively constant sex drive, they are like chimps in that female fertility is readily apparent through external signs.)

Thinking about humans naturalistically, this makes a fair amount of sense from an evolutionary point of view. The exceptionally long period it takes for human offspring to reach maturity, and the importance of learning social/cultural patterns in order to function maturely as a human, makes rearing by stable family groups highly desirable. Other higher primates, with their visually obvious mating periods, do not tend to form strong pair-bonds between mates. Indeed, quite the contrary: because a female's fertility is obvious to all males, the tendency among chimps, gorillas, etc., is for any adult male who can get within reach of her to try to get his genes into play. There are a number of different approaches a male primate may use in order to try to assure he is the one who succeeds in fathering a child on her, but there's a fair amount of competition and free-for-all involved. For humans, since it isn't immediately obvious when a woman is fertile, a male stands the best chance of passing on his genes by forming a longer term, exclusive relationship, since it's only by having relations consistently over at least a month (and knowing that other males have not succeeded in getting in on the action) that he can have reasonable assurance of being the father of any offspring. Take this relative exclusivity out into years instead of months (with the incentive of successfully fathering multiple offspring) and you've solved the problem of having both parents around to help rear offspring which take a long time to mature.

Evolutionarily speaking, there are differing incentives for men and women, which can be used to sketch different stories about men's and women's sexual drives and instincts. But I don't think it's overly controversial to assert that a compromise which suits both sets of drives well is found in monogamy, serial monogamy or polygamy -- relationship dynamics which are exclusive and stable, though not necessarily equal. (As the prevalence of polygamy in many cultures illustrates -- there's nothing but upside for a male from an evolutionary point of view if he can have exclusive access to multiple women rather than just one.)

All of which is a long way of coming around to this basic point: Uncertainty about when conception can result from intercourse is a factor which has been central to shaping the development of human sexual and relationship dynamics throughout the existence of our species.

Evolution vs. Responsible Parenthood

The above discussion should immediately bring to mind a contrast between our modern attitudes toward reproduction and what in anthropomorphic terms we might term evolution's "motivation": A host of messages in our modern society tell us that we should limit the number of children that we have, while "evolutionary success" is based upon the number of grandchildren one has who survive to reproduce. Thus, while the instincts and physical characteristics of most animals seem centered on maximizing the number of offspring, those of us in modern society tend to focus on not having more children than we plan on (and often plan on few.)

It's common for Christians of a ruralist tenor to attribute this to modern industrial society, asserting that in an agricultural society children are an asset while in an industrial society they are a liability. I think, however, this is the result of simplistic thinking. I would propose that, ever since we became aware, humans have always sought some degree of "responsible parenthood", though it's true that the cultures of many modern developed nations are much more biased against childbearing than most throughout history. Still, even in societies in which large numbers of children were described invariably as a blessing, we as humans have, because we are conscious and see death and deprivation as evils, always sought to have the "right" number of children for a given time and place.

Evolution is a process which optimizes the success of populations, not of individuals. As such, it is evolutionarily advantageous for members of a population to produce more offspring than their environment is easily able to sustain. This achieves several advantages: More individuals means more genetic variation, thus providing a larger chance for the development of advantageous new traits. Large numbers of individuals also protect against unforeseen catastrophes and provide individuals able to exploit unforeseen opportunities (new niches, migration, competition, etc.) If available resources prove not to be enough, the least fit individuals will die off, which for the genetic population as a whole is also generally beneficial.

However, we as conscious and moral beings obviously don't want to see people suffering for lack of food or other necessities. However advantageous it might be for the population, we don't want to see people suffering for lack of basic resources. And so we naturally want to avoid having children at times when we think we cannot support them.

[to be continued]

Part 2

Wednesday, March 31, 2010

The Sex Life Fallacy

[This is a re-post of a post from back in 2007, as prelude to developing some further thoughts on the topic.]

A couple weeks ago I wrote a bit about bonobos, the "sexy ape" which is sometimes referred to as the kinder, gentler counterpart to the sometimes violent chimps. A commenter later pointed out an article written by primatologist Fraans de Waal in the eSkeptic (an organ of the Skeptics Society) taking exception to the New Yorker article which inspired my post, in which article he was presented as something of an outlier, reaching exciting but perhaps somewhat exaggerated conclusions based on research only on bonobos in captivity.

It seems that Dinesh D'Souza had written a blog post based on the New Yorker article, and this had pretty much convinced de Waal that the entire thing was a conservative attempt to co opt discussion of his "sexy" apes. The Skeptics brought their own ax to grind to the table, remarking in an editorial note, "it is interesting that so many people wish to deny the undeniable relationship between humans and chimps, and at the same time cannot seem to help finding political meanings in primate behavior that supports either a liberal or conservative agenda."

The de Waal article is marginally worth reading, but it strikes me that in his overall defensiveness (perhaps a combination of his less than flattering treatment in the original article and the fact that D'Souza, whom he clearly despises, picked up the story) leads him to engage in some poor rhetorical moves.

For instance, he says that all the examples of purported violence among bonobos are from captivity, and yet two of the examples in the article are recounted by Hohmann as having occurred in the wild.

On another occasion, he dispenses with what strikes me as a legitimate question as to whether or not all of the activity between bonobos which is usually described as group sexual activity for social bonding purposes is actually sexual (as in, whether the bonobos are relating to each other sexually, or just touching each other in what to humans would be sexual ways) by quoting the Bill Clinton/Paula Jones case. Clearly, that's not answering the question as to whether actions which would be sexual among humans actually carry that connotation among bonobos, and it's unfortunate to see that kind of unseriousness in response to what struck me as a pretty balanced, well researched article.

However, all this talk about whether the "hippie primate" who "makes love not war" is indeed the sort of gentle, oversexed creature that it is reputed to be got me thinking about the whole question of a "sex life".

You see, the thing that makes bonobos seem a bit unusual compared to many other animals is their tendency to engage in mating behaviors when not "in heat". While a tiny bit of this has been observed in chimps, chimp males are usually only interested in females when the females undergo the physical changes that indicate they're fertile.

In this sense, one of the things that has excited people about bonobos is that they seem to be interested in sex all the time -- just like many humans. While those of us who use NFP often note that Topic A becomes a bit more compelling during fertile periods, the signs of fertility are not widely observable among humans, and as a species we're pretty open to mating behavior at all times (headaches aside).

It's pretty common in popular culture these days to talk about the necessity of a "good sex life", a somewhat vague term which I take to mean having the openness and opportunity to have sex fairly often and enjoy it a lot. Well, that sounds pretty nice, doesn't it? And here's the bonobo to show that it's not just a human thing, it's a way that primates can get along and relieve tension so they don't fight all the time.

This fits pretty well with the human-as-mental-creature picture which has dominated our intellectual landscape since the Enlightenment. Here we've got this great thing we can do that forms close personal relationships and is a lot of fun as well. Shouldn't we all make sure to fit regular practice of it into our schedules?

Sounds like fun, but I think it fails to take into account our existence as physical creatures with biological systems that have specific purposes. There's a reason why they call them "reproductive organs", and it doesn't have to do with xeroxing.

Now this works out fine for creatures like the bonobos. Most species have a pretty scattershot approach to keeping the species going: every time you have the chance to conceive, you do; and if there isn't enough food or parental care to go around, the child dies. Most animals, left to their own devices, will get pregnant just about as often as their bodies and nutrition will let them. Pop 'em out, let 'em go.

However modern, first world, human society has managed to work itself in expected pregnancy to be very rare (and never to come unexpectedly) at exactly the same time it's decided that everyone needs a healthy and active sex life. Basically, we want to mate like bonobos, but not have every female going around the jungle either pregnant or with a small baby clinging to her back.

Modern birth control (and abortion) has made this possible to an extent, but holding mother nature in check with technology tends to add other complicating factors. It seems moderately hard-wired in humans for sex to create emotional pair-bonding, of the sort that you need between a pair of mates raising offspring that take 13-17 years to reach biological (much less intellectual) maturity. Taking the reproduction out of sex reduces the need for pairbonding, and so we provide ourselves with all sorts of ways to make ourselves unhappy why pursuing the "sex life" ideal.

I'm not saying that biological realities mean that sex should simply be a matter of closing ones eyes and thinking of England (though a vacation sounds like a good idea now that you mention it), but it seems to me that from a creature point of view we put ourselves into awkward places when we try to focus on having a "sex life" without admitting that we're really talking about a "reproductive life".

Friday, July 10, 2009

A Few Thoughts on NFP

Sometimes you run across an argument which strikes you as wrong in such a way as to crystallize and clarify your thinking on a topic. Such a case, for me, was running into this debate from last week at InsideCatholic on the topic, "Is NFP Misogynous?"

The "yes it is" argument contained the following key elements:
Assuming any methodized sexual intercourse devised to avoid pregnancy by an otherwise open-to-life-marital-couple can actually "work," who bears responsibility for the method? I seriously question whether NFP, for many, isn't a misogynous practice -- imposing upon women an undue share of the physical and emotional burden of the theologically questionable quest of planning pregnancy.

First, we must be real. Modern NFP practices demand daily bodily measurements of women, not men.... A woman most desires sexual intimacy when she is at her most fertile.... This is also the moment when we are most likely to conceive a child. It's the moment NFP-practicing women measure and chart and predict as "fertility awareness," a "maybe-child" zone. For NFP-practicing women avoiding pregnancy, it is the moment they must say "no" to both themselves and their spouses....

I don't buy it. It sounds like a scheme to impose on women who wish to time pregnancies an almost penal practice of self-measurement, self-control, and self-denial, while requiring, at a minimum, a sort of suffering acquiescence from a spouse whose interest in the chart becomes rather strategic....

NFP needs to go the same way as the rhythm method -- which did not "work" and was, more importantly, female unfriendly. In its place, perhaps we all need to suck it up and admit what the theology asks of us: Have sex whenever you both want to... and expect a baby every time. Otherwise, don't copulate. That's a fair burden on both spouses.
The woman presenting the "no it isn't" view did a perfectly decent job of presenting the standard arguments for NFP, but I'd like to dig into one aspect in particular, especially given that by the sixth comment on the article we already see a theology student trying to argue that the "planning" involved in Natural Family Planning is really no different than the use of barrier methods of contraception since it involves "the intention of having sex without baby" and is thus "using one's intellect to create a tool which limits the possibility of procreation".

I'd like to start from a point of biological realism. The bodily organs which are used in this very pleasant thing we call sex are part of the reproductive system, which means than whenever we have sex we are performing an action which is at a biological level meant to be reproductive, in the sense that our bodies would not have this capacity were it not for the fact their function is reproductive in nature. (Interesting side note: think of all the most pleasurable things the human body can do and ask yourself, how does each one of these relate to a basic element of human survival. Generally speaking, the greater the physical pleasure, the greater the relation to survival.)

Within the overall structure of intercourse, a normal, healthy man is capable of begetting children any time he has sex. However, women (like females of virtually all other mammals) are only biologically able to conceive a few days out of the month. (Both of these reproductive strategies make a lot of sense for the individual and the species as a whole at the evolutionary level, but I don't think it's necessary to go into all that here.) Even at the "right time", a woman may or may not conceive as the result of having intercourse. Conditions have to be right for the sperm to reach the egg, the egg has to be healthy, and the sperm has to successfully implant. What this boils down to is that while the probability of getting pregnant from any one random act of intercourse is perhaps 1-10% depending on the people involved, having sex frequently will almost invariably result in pregnancy unless there is a health/age problem involved.

Other creatures, our non-rational brethren in the animal kingdom, do not worry about when they should not reproduce. Driven by instincts and natural compulsions, they mate when it is their season, have as many offspring as they can, and hope (if one may apply that word to the unthinking) that those offspring will thrive. If there are not enough resources to go around, the young, weak, and old die off. We humans see this kind of suffering as something to be avoided, and so human societies in all times and places have striven not to outgrow their resources -- using methods ranging from self denial to slaughter.

From a Catholic point of view, human life is sacred and thus abortion and infanticide are completely unacceptable as means of population control; and the sexual faculties have a moral integrity resulting from their relation to the creation of new human beings and so the sex act should not be modified (as with birth control) to remove its inherent fertility. Thus, for Catholics, the answer to the need not to have more children than one can provide for is to have sex less. Because sex has a clear and inherent reproductive aspect, which we consider it wrong to try to circumvent artificially, if you want to not get pregnant you will have to avoid having sex at least some of the time.

Now, this is where the question of whether Natural Family Planning (NFP) as practiced by modern Catholic couples is "natural" comes in. The woman's body gives certain signs of when it is likely to be fertile. These signs are rather less obvious than those of many of our fellow mammals. Female chips, for instance, have a large pink swelling around their genital area when they become fertile, such that one can tell if she is fertile from quite some distance away.

Signs of human female fertility are much more subtle. (The evolutionary reason for this would make a very interesting inquiry, I can think of a few very interesting reasons.) However they are now pretty well understood and easily learned.

So, what are the options for the Catholic couple who are seeking to remain true to the Church's understanding of human sexuality and the human person and also seeking to avoid having more children then they can raise and support?

Ms. Campbell advises, "Have sex whenever you both want to... and expect a baby every time. Otherwise, don't copulate. That's a fair burden on both spouses."

The thing is (leaving aside the dangerous problem of trying to figure out what is "fair" for both spouses in some sort of power politics sense) that this is in a sense not actually all that natural. We are not made such that sex results in a baby "every time". Sex is somewhat likely to result in a baby perhaps 30% of the time, and highly likely to do so only about 10% of the time at best. Since unlike a lot of our fellow creatures, our sex drives are not only "on" when we're fertile, the rest of the time sex serves to strengthen and deepen the bond between a couple who are going to have a lot of work and difficulty together raising children. So if you only, ever have sex when you absolutely expect to have a baby, you're actually using sex in a more minimal fashion than we're physically designed for.

If they know anything at all about their biology (from experience if nothing else) a couple is going to know they won't get pregnant every time. And knowing this, the drive is strong to say, "Surely this time is okay." Though husbands should try hard to be sensitive to the greater difficulties that pregnancy means for their wives than for them, this line of thinking is naturally going to appeal more to the man than to the woman. Desires for "fairness" aside, pregnancy is naturally going to effect the woman more directly than the man.

Given that we have the understanding of female fertility signs available to us quite easily in the modern world, it is going to cause significantly less stress without couples to use that knowledge to actually know "we might get pregnant now" versus "we almost certainly won't get pregnant now" rather than relying the more more amorphous "chances are decent we won't get pregnant this one time" or the inaccurate "we shouldn't have sex unless we're absolutely sure we want to get pregnant."

NFP works within the natural structure of what sex is -- a natural act which has both unitive and procreative elements. It encompasses self denial in that it accepts that if you want to avoid pregnancy for a while you are going to have to forgo having sex, but it provides system and achievability to that self denial by telling a couple when it is that they need to forgo sex. If you need to avoid having another child for the next year or two, you may end up having to avoid having sex nearly half the time. However, that is much more achievable and healthy for a couple than attempting to avoid it entirely for those same years -- and the differentials of fear and desire that would result from such an attempt.