A bonfire set by demonstrators protesting a scheduled speaking appearance...

A bonfire set by demonstrators protesting a scheduled speaking appearance by Breitbart News editor Milo Yiannopoulos burns on Sproul Plaza on the University of California at Berkeley campus on Wednesday, Feb. 1, 2017, in Berkeley, Calif. The event was canceled out of safety concerns. Credit: AP / Ben Margot

Last week, the post-election tensions erupted into campus violence reminiscent of the 1960s. At the University of California-Berkeley, a protest against an appearance by Breitbart senior editor and right-wing provocateur Milo Yiannopoulos erupted into riots that included assault and property destruction. (The event was canceled due to safety concerns, apparently before the violence began.) In a less high-profile incident, a College Republicans’ event at NYU, featuring far-right media figure, commentator and comedian Gavin McInnes, was also violently disrupted by protesters, resulting in 11 arrests; McInnes was attacked with pepper spray.

A number of voices on the left, from comedian Sarah Silverman to CUNY history professor Angus Johnston, have downplayed, defended, or outright celebrated the violence, portraying it as resistance to “fascists.” This is not only deplorably illiberal but shockingly stupid.

We shouldn’t have to say this, but one of the foundational principles of both liberalism and the United States of America is freedom of speech. Yes, of course freedom of speech doesn’t mean freedom from vigorous criticism. College students and others have every right to protest a speaker they find offensive. But once a protest is intended not just to express disapproval but to silence a speaker, it becomes an attack on basic rights. While the First Amendment protects us only from infringements by the government, protesters who use aggression to prevent others from speaking or hearing speech are guilty of assault or harassment — not to mention assault on the spirit of free speech.

This is true even if there are excellent reasons to dislike the speaker — such as Yiannopoulos, a narcissistic attention-seeker who has escalated his crusade against political correctness into nasty mockery of various groups and individuals. (McInnes offers a less colorful version of the same shtick.)

Claims that it’s righteous to use disruption or even violence to shut down “fascist,” “Nazi,” or “racist” speech are especially disturbing to many people who have no sympathy for fascists, Nazis, or racists because progressives often define those terms quite broadly. Today, they go after Yiannopoulos, who has arguably used his platform to glamorize the quasi-fascist “alt-right.” Tomorrow, a “fascist” could be someone who has criticized race-based affirmative action.

Here are a few more obvious points. Trying to suppress offensive speech usually draws more attention to it. The more activists try to ban Yiannopoulos, the better his upcoming book, “Dangerous,” sells on Amazon even before publication. (After the Berkeley riots, it rose to No. 1.) Even if rowdy protests can deter people from attending an event, they can help the speaker build an even bigger following online.

Worse, violence may well lead to an escalation of violence. What happens when more Trump fans start bringing guns? (At another recent Yiannopoulos appearance, one of his fans non-fatally shot a protester and claimed self-defense; the Berkeley fiasco will boost such claims.) And if progressives believe the Trump White House wants to squash civil liberties, why provide the perfect pretext?

Last but not least, using violence tends to make your side look bad. A video clip that shows a young female Donald Trump supporter (and Yiannopoulos fan) getting randomly pepper-sprayed in the face by a protester does not help the “resistance”; it only accomplishes the difficult feat of giving Yiannopoulos the moral high ground.

Normally, if I were an adviser to a campus conservative, Republican, or libertarian group, I would strongly recommend not inviting a speaker who traffics in outrage rather than intelligent discourse. But when that speaker becomes a target of violence, such advice looks like caving to intimidation and betraying free speech. Thanks, protesters.

Cathy Young is a regular contributor to Reason magazine and Real Clear Politics.