Once again, the supposedly anti-fascist Antifa movement has reared its violent black-cloaked head.

On Sunday, Antifa supporters attacked a group of conservative protesters in Berkeley, California who, to all appearances, have nothing to do with the white nationalism or supremacism of the group that marched in Charlottesville earlier this month.

YouTube is filled with videos from the event showing peaceful gatherers being accosted by weapon-wielding Antifa thugs. One video posted by Mother Jones reporter, Shane Bauer, shows a mob attacking a man as he curls up on the ground. In another video posted by the journalist Ziva Branstetter, Antifa protesters are seen chasing down two conservative marchers. None of these victims were affiliated with white supremacist groups.

I have two takeaways.

First, Sunday's events are yet more evidence of an unyielding truth: Antifa are violent fascists, not anti-fascists. American-Antifa followers bear no hesitancy in replicating European "black block" efforts to conceal their identities and carry sticks as weapons. Unfortunately, many on the Left seem to quietly celebrate this unpleasantness: note that Bauer's video of the mob attack received thousands of Twitter likes.

That's a big problem, because Antifa's violence isn't just localized criminality. It is a coordinated assault on freedom of speech and thus fundamentally incongruent with the U.S. Constitution.

My second takeaway is the decision, as the San Francisco Chronicle's Lizzie Johnson reports, of Berkeley Police to deliberately allow Antifa to attack the permitted protesters. The police defended this neglect of duty stating, "We made a strategic decision to move our officers, we also want people to freely assemble."

But let's be clear, this is a pathetic excuse, and we've been seeing a lot of it lately. The first responsibility of the police is public protection, and free assembly does not exist where it is subjugated to the whim of a violent mob. It's not fair to blame the police alone -- Berkeley's notoriously liberal city government also shares outsize blame here. As in Charlottesville, it seems likely that the Berkeley city government pressured the police not to take action. After all, in the run up to the conservative protest, the city printed 20,000 leaflets implicitly blurring these protesters with those of the alt-right. Those leaflets read "Berkeley stands united against hate."

That casual ignorance speaks to the broader issue: a growing understanding from many on the Left that any peaceable assembly they disagree with is illegitimate and unworthy of constitutional protection. Such thinking is exemplified by Mr. Bauer, who, in addition to posting the video of the mob attack, posted this tweet.

Bauer, Berkeley, and all their supporters are wrong. By tolerating the idea that some individuals are not entitled to practice their right to freedom of assembly, we lend credibility to the idea that they are legitimate targets for violence. In doing so, we excuse government failures to protect the rights of our fellow citizens and the sanctity of our democracy.