It was a sad day for the First Amendment at the University of California, Berkeley: militant far-left students stormed the stage during a recent forum featuring Metallica drummer Lars Ulrich, fully intent on halting the event. Their actions—which included an alleged assault of one of the other speakers—are not merely a betrayal, but a repudiation of the values of the university that birthed the Free Speech Movement in the 1960s.

In an election season when U.S. political discourse has been profoundly damaged by an increasing contempt for free speech—both among the liberal hecklers who disrupt Donald Trump events, and among Trump’s own supporters and campaign staffers, who respond with violence—it’s more important than ever for universities to serve as bastions of tolerance and free expression. But if the episode at Berkeley is any evidence, universities have become breeding grounds for the illiberal values now permeating American society.

The Berkeley episode involved the Student Labor Committee, a group of liberal students who believe that the university administration treats its contract workers poorly. The group has demanded better wages for these employees and is urging prospective speakers to boycott the university until the administration caves.

Whether or not the students are right about employee compensation, they have every right to press the university for better treatment. They also have the right to boycott events, and to urge others—including the planned speakers for these events—to do the same. This is the very essence of political action.

But calling for boycotts and enacting actual censorship are very different things—especially when violence is used. Which brings us to the Ulrich event.

Ulrich, who is known for holding quasi-libertarian views, was hosting a forum on campus to “celebrate the creative culture of the Bay Area,” according to the Foundation for Individual Rights in Education. Ulrich was joined on stage at different times by other notable people, including Salesforce.com founder Marc Benioff, Ulrich’s own father, and others.

Well aware that aggrieved students did not want the event to proceed, Ulrich began the event by inviting them to speak. One did so. The event then continued.

But the activists were still intent on derailing the event, and eventually they stormed the stage. Their goal was to enact the heckler’s veto by making the event too unsafe to continue. To that end, one student actually attacked Benioff, according to an op-ed in The Daily Californian that described the incident as “a shocking, vicious spasm, which fortunately did not result in any injuries—after which the show went on (as it must).” This student’s attempt to wrestle the microphone away from Benioff was captured on video.

Campus police were on hand, and intervened in time to prevent anyone from being hurt. Thankfully, the students did not succeed in their effort to derail the proceedings. But the mere fact that they tried—that they believe in violence and the heckler’s veto—is a serious indictment of their movement.

The incident would be worrisome enough if it were merely an isolated incident. Unfortunately, the University of California system is rife with examples of illiberal students refusing to let anyone else discuss ideas that they don’t want to hear. Recently, at the University of California-Davis, pro-choice protesters disrupted a pro-life demonstration by confiscating their flyers and throwing them on the ground. The perpetrator was caught on camera and was approached by police, but escaped without punishment.

Far too often, the universities themselves deserves blame for either humoring students’ censorious delusions or taking matters into their own hands. At another California university, California State University of Los Angeles, administrators told conservative students that they couldn’t bring right-wing pundit Ben Shapiro to campus unless they balanced out his perspective by also including a liberal voice. This is, of course, nonsense.

The administration eventually relented and allowed the event to proceed—at which point, crazy students took up the effort to violate Shapiro’s First Amendment rights at all costs. Protesters mobbed the event—injuring some spectators—and even pulled the fire alarm multiple times in an effort to shut it down.

Perhaps Shapiro’s firsthand experience with illiberal violence and thuggery informed his decision to stand with his former Breitbart colleague Michelle Fields, who was recently assaulted not by liberal protesters, but by a member of the Donald Trump campaign. Both Shapiro and Fields have resigned from Breitbart because the organization took Trump’s side rather than hers.

Violent disrespect for the First Amendment—the crowning achievement of civil society—is not solely the province of the left or the right. Sadly, it seems like an increasingly common trait of activists on both sides.

Trump recently canceled a planned event in Chicago out of concerns that leftist demonstrators who took over the event had made it unsafe. Of course, Trump’s own supporters often behave just as badly. Who can forget the man who punched a restrained Black Lives Matter protester in the face?

Politically engaged people of all stripes are turning their back on the most important right in American society: the right to speak without fear of violent repression. It is a terrible tragedy that we evidently cannot trust our public universities to serve as moral compasses leading us back toward civility.