To many observers, the Catholic hierarchy’s opposition to birth control seems nonsensical — they might as well oppose ice cream. It seems like a win-win: the liberals are happy that women get reproductive freedom, but meanwhile if you’re anti-abortion, it seems like avoiding unwanted pregnancies in the first place is the best possible solution. What’s not to like? Or more to the point: why are they making this, of all the many Catholic moral teachings, the cross they’re willing to die on, even as the laity has long since stopped caring?

I don’t think we can explain this simply through misogyny or fear of feminine sexuality, etc., because there are plenty of misogynists in the world who don’t make a point of picking a fight with the president of the United States over birth control. This birth control issue seems to be almost exclusively a Catholic “thing,” so it has to have a Catholic-specific explanation. I propose that the answer can be found in a historic compromise set forth by one of the most influential thinkers you’ve never heard of: namely, Clement of Alexandria, a second-century Christian philosopher.

In the history of the Catholic Church, Clement’s compromise was arguably almost as defining a moment as Paul’s declaration that Gentile Christians were not obligated to meet Jewish ritual requirements. The point at issue was of course not birth control, but whether marriage should be permitted for Christians. This question makes sense in light of the fact that Jesus and Paul, the two major founding figures of Christianity, were themselves celibate — and in the Roman world, counterintuitive as it seems to us now, there was a huge attraction in celibacy. The sects of Christianity that required celibacy actually grew much more rapidly than the more moderate versions.

At the same time, a celibacy requirement obviously presented a huge obstacle if Christianity was to be a mainstream movement, since it automatically excluded many people (including many of the rich and powerful, whom Clement was eager to court). Possessing the Catholic instinct for having things both ways, Clement came up with a solution: celibacy would be the elite path, but marriage would be permitted for the average believer.

Unlike Paul, who permitted marriage purely as a release of sexual tension, Clement’s rationale for permitting it was to limit sex to reproductive purposes. In this, he was following the prescriptions laid out in Plato’s Laws (which he weirdly believed to be inspired by Moses) for bringing the sexual drives under the control of reason. He believed (or at least said) that there was a real danger of a slippery slope and claimed that there were some Christian sects that allowed a total sexual libertinism, which was throwing the movement into disrepute. Hence the need to limit sexuality to its obvious and natural purpose: reproduction.

This compromise obviously had its influence in the East as well, but its effects were arguably more intense in the West, where all clergy were eventually required to be celibate. Over the course of the Middle Ages, the stigmatization of non-reproductive sexual activities (including homosexuality) picked up speed, resulting in the invention of the category of sodomy. (Fun fact: Tertullian, a theologian writing at roughly the same time as Clement, argued that the sin of Sodom was indulging in marriage.) Toward the end of the Middle Ages, marriage was ultimately enshrined as a sacrament, cementing the two-tiered system as the basis of day-to-day Catholic experience. The shock of the Reformation, which combatted the requirement of priestly celibacy, only led to a further entrenchment of clerical celibacy during the reactionary period of the Counter-Reformation.

Fast forward to the aftermath of Vatican II, where a spirit of reform and openness to the modern world dominated — and one of the innovations of the modern world was of course The Pill. A council of experts recommended that the Catholic Church change its anti-contraception stance, but in 1968 the pope rejected their recommendation and reaffirmed the status quo in the infamous encyclical Humanae Vitae. In retrospect, this moment could appear to signal the premature death of the “spirit of Vatican II.”

This is strange: in the wake of Vatican II, the Catholic hierarchy was willing to make radical changes to the liturgy, to dethrone Thomas Aquinas as the standard of all theology and philosophy, to rethink its stance toward other religions, etc., etc. Why go to war over such a small and seemingly harmless issue?

I’d propose it’s because it went deeper than ideas: it was about day-to-day life. It was about the base-level way the Catholic community was structured — including the legitimation of the hierarchy’s authority. All of that depended on the notion that sex should be limited to its “natural” purpose of reproduction and otherwise avoided. What widespread dissemination and normalization of birth control threatened to do was decouple sex and reproduction — and also make sex seem less “dangerous,” less in need of control. The entire rationale behind Clement’s compromise and hence the entire rationale behind the way the Catholic community had structured the most intimate aspects of its day to day life would be totally destroyed.

In the face of that threat, the Catholic hierarchy basically decided to pretend that the advent of birth control had never happened — that it was some kind of aberration rather than a normal fact of modern life. The fact that they allow the practice of “Catholic family planning” based on timing the woman’s menstrual cycle is not hypocritical within this horizon: the Catholic Church has always tacitly allowed loopholes to lessen the severity of its rules, and this is a naturally-occurring loophole that doesn’t fundamentally change the relationship between sex and reproduction. It relies on the natural operation of the woman’s reproductive system, whereas artificial birth control works by disrupting that natural operation.

So the reason the Catholic hierarchy views issues of sexuality as their Rubicon is because it strikes at the heart of that hierarchy’s own self-legitimation and day-to-day life experience. It may not be an exaggeration to say that the hierarchy views Clement’s compromise as something almost as fundamental as Paul’s refusal of conversion to Judaism for Gentile believers. The threat is just as great as if a council of theologians was suggesting that the Catholic Church should require believers to convert to Judaism after all — the very basis for a separate Christian structure of authority would be utterly destroyed.

The fact that this insistence is gradually alienating the hierarchy more and more from the laity and thus undermining its authority is no counterargument: I’m pretty sure the hierarchy thinks they can wait this out.