For more than half a century, at least since the invention of the birth-control pill, secularists and progressives collectively, if not always consciously, have been assembling a new, quasi-religious orthodoxy. In place of the Judeo-Christianity of yesterday, and mimicking its outlines to an uncanny degree, this new body of belief has by now a well-developed secular catechism. Its fundamental faith is that the sexual revolution -- that is, the gradual de-stigmatization of all forms of consenting non-marital sex -- has been a boon to all humanity.

In the new dispensation, traditional restrictions and attitudes are viewed as judgmental, moralistic forms of socially sanctioned aggression, especially against women and sexual minorities. These victims of sexuality have become the new secular saints.

Their virtue becomes their rejection and flouting of traditional sexual morality, and their acts are effectively transvalued as positive expressions of freedom. The first commandment of this new secularist writ is that no sexual act between consenting adults is wrong.

Two corollary imperatives are that whatever contributes to consenting sexual acts is an absolute good, and that anything interfering, or threatening to interfere, with consenting sexual acts is ipso facto wrong. Note the absolutist character of these beliefs as they play out in practice.

For example, it is precisely the sacrosanct, nonnegotiable status assigned to contraception and abortion that explains why -- despite historical protestations of wanting abortion to be "safe, legal, and rare" -- in practice, secularist progressivism defends each and every act of abortion tenaciously, each and every time.

Tellingly, this new faith will not even draw the line at what is known as "partial-birth" abortion, a practice that even the late senator Daniel Patrick Moynihan, a liberal who was no ally of traditionalists, once called "close to infanticide."

Yet even partial-birth abortion does not sway the conviction of activists who defend it. If abortion were truly an exercise of "choice," one would logically expect its defenders to choose against it sometimes. But this, to repeat, does not happen -- and that it doesn't tell us something about where secularist progressivism is coming from. Abortion is not a mere "choice," in the value-free consumerist way that rhetoric frames it.

No: Abortion within secularist progressivism has the status of religious ritual. It is sacrosanct. It is a communal rite -- one through which, it seems safe to speculate, some people enter the secularist-progressive community in the first place. Secularists and churchgoers alike need to understand the inner logic of today's animus against religious believers. If the fury directed at them and their precepts could be pressed into a single word, that word would not be theodicy. It would not be supersessionism.

It would not be Pelagianism, Arianism, or other religious casus belli of the past.

In the contemporary Western world, that single word would be sex. Traditional Christianity present, like Christianity past and Christianity to come, contends with many foes and countervailing forces. But its single most deadly enemy now is not the stuff of the philosophy common room. It is instead the sexual revolution -- and the current absolutist defense of that revolution by adherents and beneficiaries.

After all, Christians and other social dissidents today aren't threatened with job loss because of writing in self-published books about the biblical teaching against stealing, say. Military chaplains are not being removed from office and sidelined for quoting from the book of Ruth.

No, every act committed against believers in the name of today's intolerant "tolerance" has a single, common denominator, which is the secularist protection of the perceived prerogatives of the sexual revolution at all costs. The new intolerance is a wholly owned subsidiary of that revolution.

No revolution, no new intolerance. Today's secularist progressivism is not a nihilistic worldview. To the contrary: It embraces an alternative orthodoxy and a well-developed body of beliefs. What also needs understanding is that pace the suspicion of some traditionalists, today's secularist progressivism is not a nihilistic worldview.

To the contrary: It embraces an alternative orthodoxy and a well-developed body of beliefs. The fundamental impulse leading to the penalizing of moral traditionalists today is not libertarian. It is instead neo-puritanical -- that is, it is aimed at safeguarding its own body of revealed and developed truths, and at marginalizing, silencing, and punishing competitors. This substitute religion mimics Christianity itself in preternatural ways.

It offers a hagiography of secular saints, for example, all of them patrons of the revolution: proselytizers for abortion and contraception, such as Margaret Sanger and Helen Gurley Brown and Gloria Steinem; crypto-scholastics whose work is revered by generation after generation of the faithful and off-limits for intellectual revisionism, such as Alfred Kinsey and Margaret Mead; quasi-monastic ascetics, such as the grim public custodians of the National Abortion Rights Action League and Planned Parenthood; and even foreign "missionaries," in the form of representatives within progressive charities and international bureaucracies -- those who carry word of the revolution, and the secularist sacraments of contraception and abortion, to women in poorer countries around the world.

Similarly well-developed is the demonology of this substitute faith, which now includes, say, the Roman Catholic hierarchy; the major spokesmen for evangelical Protestantism; legal groups involved in religious-liberty cases; most political conservatives; all social conservatives; and the occasional apostate who deviates from the secularist code. The followers of this newfound code further accept as Holy Writ a canon of texts and doctrine -- a body of literature and commentary that cannot be questioned without risk of excommunication from the group. It is also ruled by a certain kind of logic -- not Aristotelian logic, but some other kind, whose syllogisms include "if you are against abortion, therefore you are anti-woman"; "if you oppose same-sex marriage, therefore you hate people attracted to the same sex"; and related formulations that Aristotle himself would rule fallacious.

Whether the close overlay between the architectonic of secularist progressivism and Judeo-Christianity itself speaks to the inescapabilty of two thousand years of religious history, or rather to the resonance of those religious traditions themselves with the deepest and most ineradicable human longings for transcendence -- or both -- is a fascinating subject that deserves to be explored.

But that today's progressive ideology shares recognizable features with Judeo-Christianity, even as it repudiates all traditionalist tenets that threaten its substitute theology, seems beyond dispute. The bedrock of contemporary progressivism can only be described as quasi-religious.

The followers of this faith are, furthermore, Kantians regarding these beliefs, in the sense that the philosopher's categorical imperative applies: Exactly like followers of other faiths, they believe both that they are right, and that people who disagree are wrong -- and that those other people ought to think differently. The so-called culture war, in other words, has not been conducted by people of religious faith on one side, and people of no faith on the other.

It is instead a contest of competing faiths: one in the Good Book, and the other in the more newly written figurative book of secularist orthodoxy about the sexual revolution. In sum, secularist progressivism today is less a political movement than a church.

Mary Eberstadt is the author of It's Dangerous to Believe: Religious Freedom and Its Enemies, published June 21, 2016 by HarperCollins. This essay is adapted from the book.

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