Sex should never be reduced to its physiological features. While the vast majority of human sex acts do not result in procreation, they are naturally ordered to the forging of ties between partners. To understand human sex is to focus first on its effects on whole persons, not on its biological outcome. This is the second way the vision of sex in Humanae vitae is unnatural: the criteria for acceptable methods of spacing children were described in terms not of the people involved, but of the physical act only. The whole person’s development as a sexual being in relationship with others was counted as less important than where and when a man ejaculates. And in a move away from Catholic moral tradition since Aquinas, the intention of the couple’s act was subjugated to a consideration of its physical structure.

The corrosiveness to marriage of an NFP-only approach was reported to Paul VI’s birth-control commission. Commission members Pat and Patty Crowley surveyed thousands of Catholics: most said that the rhythm method—an earlier, less effective version of today’s NFP—had harmed their marriages. Then as now, there have been those who find NFP a joyous and fulfilling way to space their children. Most Catholics, however, ignore the church’s prohibition of artificial contraception as irrelevant. As theologian Lisa Sowle Cahill said: “I am confident that most Catholic couples would be incredulous at the proposition that the use of artificial birth control necessarily makes their sexual intimacy selfish, dishonest, and unfaithful. Nor is their valuing of parenthood based on their experience of isolated sex acts as having a certain procreative structure.”

Humanae vitae also presumes a degree of self-determination that many women do not enjoy, especially (but not exclusively) in the developing world. Paul VI warned that contraception would leave women vulnerable to sexual exploitation by men. Sadly, such abuse long predated the Pill. What reliable contraception does—especially contraception that women control—is give women greater determination over their reproductive lives, even if their partners are indifferent to their well-being and that of their children. What Humanae vitae described as self-indulgence sounds to many women like self-defense, or at least self-care and more responsible parenting.