Every revolution triggers a counterrevolution. And a counter-counterrevolution ... ad infinitum, until everyone collapses in an exhausted heap.

And so with campus free speech. First came the treatises on “microaggressions,” the safe spaces, and finally the assaults and the flames. Then anxious conservative think-pieces wondering if the toxic miasma of progressivism had finally destroyed students’ minds. And then left-wing writers arguing that said writers were losing their minds over a phenomenon that didn’t matter enough to merit remark, and regardless wasn’t happening.

Who’s right? Well, astute readers will have noticed that this is actually two questions: “Is intolerance of speech actually increasing on campus?” Followed by “If so, why should we care?”

At Heterodox Academy, a site devoted to ideological diversity on campus, Sean Stevens and Jonathan Haidt dive into that first question. The answer they come up with is: Yes, support for free speech really does seem to be decreasing among the current generation of college students. And presumably as a result, speech-chilling activity is increasing.

The number of students agreeing with the statement “The climate on my campus prevents some people from saying things they believe because others might find them offensive” increased between 2016 and 2017. Surveys find that current college students are more likely to express support for speech restrictions, and less for the benefits of free speech, than graduates. Virtually everyone on campus seems to agree that politically conservative views are restricted more than liberal ones, and conservatives are more likely to report self-censorship than members of the left. And while the rate of successfully disinviting speakers or disrupting speeches is low, it has risen in recent years, with all of that increase coming from the left.

To be clear, we’re not talking about Maoist China; even most Republicans think it’s possible for their ideas to be heard on campus. And the trend is of short duration. Survey data is inherently noisy, so it’s possible that the trend may turn out to look, in retrospect, more like a blip.

Yet at the moment we’re left with the disinvitations and the heckler’s veto (most recently against law professor Josh Blackman at the City University of New York), and occasionally, the vandalism and assault. These incidents do seem to have risen recently, even if they’re not an everyday occurrence or a long-term trend. Which leaves us with the question: How much should we care?

The answer, of course, is something like what conservatives might say about the more vivid examples of campus speech suppression: that these things are the little tip of a vast iceberg lurking beneath the waterline. That for every group of hecklers shouting down a speaker or ritually humiliating a professor and that happens to be caught on camera, there may well be thousands of other less noticeable interactions producing the same effect with less spectacular means. And that when the ocean these icebergs are floating in consists of some of our most culturally powerful institutions, the custodians of our Gross National Intellect, they can be dangerous indeed.

The big cost of what antifa did protesting Milo Yiannopoulos at Berkeley is not the property damage, or even the hefty security bills universities are now paying to host controversial speakers. It’s the future invitations that won’t be issued, the people who started to speak their minds, then thought the better of it.

Of course, if you think that those people shouldn’t speak their mind, then that “cost” may look more like a benefit. But many of us still think that the great liberal compromise that ended Europe’s wars of religion — “I don’t like what you say, but will defend unto death your right to say it” - is one of humanity’s noblest inventions. We think that this made the Enlightenment possible, and all the flowering of human thought and invention that followed it. We might also point out, a little puckishly, that it created the modern left.

But more seriously, we’d note that liberalism let groups of people with radically different answers to life’s most vital questions live together without killing each other. And ask those who would break that truce to remember the real perils that an overzealous consensus presents for everyone, including the true believers. If you declare holy war, you’re apt to get an unholy one. And if you make your Inquisition too powerful, eventually you get Martin Luther.

Megan McArdle is a Washington Post columnist.