Semester after semester, year after year, tensions on college campuses have escalated, with intolerance of dissent climbing to darkly censorious levels.

Facing Trump-fueled rage and censorship from campus leftists, conservative students reacted by bringing in the most offensive speakers possible, such as Milo Yiannopoulos. At the University of California, Berkeley, this rhetorical bomb thrower's opponents lit real fires and smashed the place.

Then at Middlebury College in March, protesters against Charles Murray, the conservative social scientist, disrupted his event so that he simply could not speak. They did not want debate. He was obliged to give his address on video from a secret location, but even then, student radicals hunted him down, rushed him and a Middlebury professor on a dark campus walk, and jostled and intimidated them, injuring the faculty member, who had to wear a neck brace as a result.

Students got on top of the hood of the car Murray was in, shouting and acting out in the uncivilized way that so many misguided people have come to regard as a manifestation of a social conscience.

It was a dark moment for academia, and most observers expected things to get worse. Speech was now condemned as violence, and violence (in an ideologically vetted cause) was speech. Dissent was no longer patriotic, and free speech was no longer a virtue.

So, tensions were high this fall as students returned to school just weeks after the violence in Charlottesville and a summer filled with political chaos. Bracing for tumult, Berkeley poured $600,000 into security for an hour-long lecture by Ben Shapiro, a mainstream conservative author. Images from campus before Shapiro’s appearance recalled a war zone.

But tensions fizzled, and nothing of real consequence materialized. Perhaps that set the tone for the whole semester. For no professors appear to have landed in the hospital with wounds inflicted by anti-speech leftists, and no violent “anti-fascist” mobs appear to have caused six-figures worth of damage to any university. There has, it goes without saying, been no correction of rampant liberal bias in higher education. But Middlebury and Berkeley may not have been harbingers of a dark future, and they could, indeed, turn out to be the darkest moments before the dawn.

Could it be that spring semester 2017 will turn out to have been a watershed, a turning point, the moment when campus radicals finally went too far and the forces of free speech began to push back effectively?

The Foundation for Individual Rights in Education released its annual survey of campus speech codes this week, and there was good news for proponents of free expression in the academy. The percentage of schools maintaining “severely restrictive” codes, categorized as “red light” codes, declined for the tenth year in a row, falling seven percentage points even from last year’s number. But “the best news,” according to FIRE, is that “an unprecedented number of schools have eliminated all of their speech codes,” earning the organization’s highest “green light” rating.

Most of the 461 schools surveyed by FIRE fell somewhere in the middle, with nearly 59 percent earning “yellow light” status, meaning “their policies still chill or outright prohibit protected speech, albeit to a lesser degree than at a red light institution.”

The suppression of thought and expression on campuses therefore remains a bleak reality, but perhaps it is improving. The pause in anti-speech violence is a small cause for celebration.

But it is no cause for complacency.

The cause is advanced when the forces of open debate defend pluralism and free speech, winning over those who may not be ideological allies, but still want a fair fight. It is made well by inviting people such as Murray to air their views and listening respectfully to them. The cause is advanced when people, through their arguments and reason, demonstrate the value of hearing other perspectives.

These efforts, we can hope, have made campuses a bit more open, and if we continue in the vigilant defense of liberty, censorship and intolerance can be forced to retreat.

Allowing or welcoming dissenting opinions would, however, be the beginning, not the end, of a desirable re-enlightenment. When, in some distant future, higher education routinely favors free expression, it will at last be receptive to the idea that the academy's role should not be to prime impressionable students to discredit any idea to the right of Noam Chomsky. That's a battle conservatives want to join. In the battle of ideas, conservatism wins not least because, as Margaret Thatcher said, the facts of life are conservative.

That's why the Left doesn't want anyone to hear from the other side.