The Catholic Church sanctions a form of family planning in which the couple has sex only in those times of the month when the woman is naturally infertile. Why?
This reason is that a woman who uses contraceptives does not fully give herself to her husband. She is saying: “You can possess me, but I won’t let you beget a child in me.” She can conceive but refuses to do so.
With the “natural” planning, this technically does not occur. There is either no love and no children, as in when the woman is fertile, or love and children, except it so happens that nature prevents conception.
The problem here is that praxeologically, this may seem to be a distinction without a difference. Does it matter whether conception is checked by the woman’s body alone or body plus a contraceptive pill? In both cases, there is the same intention on the part of the husband and wife, namely, to enjoy sex without the possibility of making a child.
Now God made the woman’s body in a certain way. She is fertile on the 4th and infertile on the 24th. When the couple has sex on the 24th, God is preventing conception, as per His own design. When the woman takes a pill on the 4th, she takes matters into her own hands.
But what’s wrong with that? God has designed humans such that their hair grows. Is it wrong to have a haircut? Life is naturally solitary, poor, nasty, brutish, and short; what’s wrong with building a civilization? The difference is that getting haircuts is due to an individual’s regard for himself, while sex is bound with individual regard for the species. People are naturally eager to seek their own happiness. Maintaining the human species is something quite different from that. It requires distinct sacrifices of purely individualistic pleasures. Children are “flowers on our graves.” Too much egoistic self-regard, and there may not be a next generation at all. Hence, it seems that procreation cannot be fully under exclusive human control but is something that is in part managed by God.
Hence, humans are not entirely free and autonomous in pursuit of sex and love. They must give their due to God. Using contraceptives entails taking an excessive share of control over procreation.
But what if God had designed humans in such a way that the woman was fertile always? Would not that have spelled the end of natural family planning? Isn’t NFP, therefore, based on an accident, a kind of loophole in the divine laws? And what if our couple wanted to have sex on the 4th not on the 24th? Why should it have to wait, just because of this accidental obstacle? God’s design seems arbitrary and flawed.
Regarding the first question, who says the design is accidental? Perhaps God in his great mercy has enabled NFP to enhance the unitive function of sex at some expense of the procreative function. Regarding the second question, again, the answer lies in a certain conflict between the interest of individuals and the species as a whole; or if you like, between the presently living and those yet unconceived. Sometimes the former should yield to the latter.
We may, if we like, make this more concrete. For example, suppose there is pre-existence of the soul. There is a long line of souls in heaven waiting to be called to incarnate as humans and live this life. Without procreation, their interests, which include our own, if there is such thing as re-incarnation, will be hurt. We should be mindful of the interests not only of this world but of the universe as a whole. The yet unborn have a claim on us.
Even if the unconceived cannot be said to exist, we the living may desire a large communion of saints. Not 10 people but 10 billion people. But in that case it pays Smith not to have children but benefit for free from Jones’ children. But everybody thinks this way. This is a case of positive externalities unrealized. Children are underproduced. One possibility is to have the state subsidize large families. But we live, or want to, in a free society. It is immoral to tax childless people for the sake of those with children. Further, under such conditions, children will be viewed as a means to government hand-outs rather than loved for their own sakes. Hence, the Church’s moral suasion seems like the best possible solution.
In short, going no further then NFP is a concession to God’s will regarding the well-being of the species. And that is the point of the Catholic Church’s injunctions.