Herbert Marcuse, of the Frankfurt School of critical theory, published an essay in 1965 with the provocative title “Repressive Tolerance,” in which he argued that “liberating tolerance” would entail “the withdrawal of toleration of groups and assembly from groups and movements” on the right, while encouraging all aggressive movements on the left. His dream, it would seem, has come true.

Use the wrong word, have a political flaw in your past, fail to line up for the next obviously good cause, and the tolerant will be the first to come after you. They may not be able to burn you at the stake, à la the Spanish Inquisition, but they will make sure you don’t get the job, promotion, prize or leg up. They will instead see you castigated, fired, consigned for life among the mean, ignorant and lumpen.

Here are five opinions and views—one could add many more—the tolerant absolutely won’t tolerate:

• That abortion is, somehow, anti-life and thus might just be wrong.

• That the final word isn’t in on climate change, let alone what, if it exists, ought to be done about it.

• That racism isn’t systemic but the absence of fathers in African-American families is, with 70% of black births being out of wedlock.

• That sexual reassignment surgery and transgendering generally is a ghastly solution to what possibly isn’t truly a problem.

• That most government programs for the improvement of the human condition are unlikely to be effective and in many cases exacerbate the illnesses they set out to cure.

People who hold these opinions are judged by those who pride themselves on their tolerance as beyond the pale, stupid, harmful if not dangerous, and utterly—thank you, Mrs. Clinton—deplorable. They are condemned as misogynist, racist, without empathy, unimaginative, ipso facto intolerant, hence not to be tolerated. They need to be put down, shamed, cast out; all that they represent needs to be squashed, crushed, canceled.

Whence does the confidence of the newly tolerant derive? Chiefly, I believe, from a strong sense of their own virtue. They are convinced they are on the right side: the side of social justice, of generosity of spirit, of sensitivity, of goodness and large-heartedness generally. They think themselves the cognoscenti, in the know, superior in every way. They are the best people, and they damn well know it.

One of the plummiest targets for attack by intellectuals in the 1950s was conformity. Conformists in those days were thought to reside in American suburbs; they were judged unimaginative, thinking dull thoughts, living out lives of quiet desperation. How it would pain the officially tolerant of our day to think themselves conformists. Yet to be tolerant today entails a strict conformity of opinion. They might wear rococo beards, ponytails and tennis shoes with tuxedos, have had 20 affairs and three abortions, and attended what the world thinks are the best schools. But they all know that, should they depart the deep grooves of locked-in opinion that is the source of their virtue, they risk social excommunication. Few are willing to risk that.

Purity of opinion is a poor test of character. In the realm of character, actions speak not only more loudly but also more profoundly than words. A standard comic figure is that of the liberal who professes a set of grand opinions and lives a richly comfortable life in opposition to them all. Opinion is necessary in the public realm for the formation of policy, but in the private realm, it can destroy friendships, divide families, and give one a vastly inflated sense of oneself. The French poet Paul Valéry called opinions the “products of intellectual flatulence,” adding that they “relieve the man giving vent to them, but pollute the intellectual air for others.”

Still, it is one thing to laud oneself for the superiority of one’s own opinions and quite another to want to destroy others for what one deems the moral inadequacy of theirs. In the current political climate, this is what those who pride themselves on their tolerance are all too happy to do. What is unprecedented, and unhappily becoming a contemporary condition, is the intolerance of the ostensibly tolerant for even the slightest disagreement. Hence the refusal of our once most august universities to allow speakers whose views their students and faculties find uncongenial. Hence the organization of what are in effect lynch parties devoted to tearing down statues and insisting on the renaming of schools and institutions. Hence the McCarthy-like search through people’s pasts for unfashionable opinions with which to destroy their reputations.

Should you encounter one of the grandly tolerant of our day, my advice is to hear him out on the perfection of his opinions, then let him know that you view him as the Jews viewed the czar—that is, he should live and be well, but not too close to you.

Mr. Epstein is author, most recently, of “Charm: The Elusive Enchantment.”