“You can’t trust anyone over 30,” some of us used to say in the 1960s. Now that I’m over 70 — and still struggling for social justice — I see there are people under 30 you cannot trust: the supposed “Antifa” (anti-fascist) groups that have, in effect if not in intent, become the secret little friends of Fox News and, ironically, American fascism.

I don’t speak lightly. We’ve seen it before: young people whose infatuation with violence undermines the progressive cause.

In the 1960s, we fought effectively and nonviolently against American apartheid and against America’s mass killing in Vietnam. I was an organizer in eastern Arkansas for the front-line civil rights group Student Nonviolent Coordinating Committee (SNCC) and an anti-Vietnam War organizer, speaker and author, arrested a number of times in both pursuits.

Enormous numbers of people came to support those nonviolent movements. But we had our Antifas, too. They called themselves “Weathermen,” and they claimed we needed to “bring the war home.”

They brought street fighting with the police and further violence to our otherwise peaceful anti-war actions. They undermined broader participation and gave political ammunition to pro-war forces. They helped elect Richard Nixon, prolonging the war for years.

Sadly, the same violent, self-obsessed mentality is at work today.

In response to the widespread condemnation of Trump after Charlottesville, white supremacists sprang to his defense, proposing pro-Trump demonstrations in Berkeley, among other cities.

On Sunday, I joined 4,000 others at a Berkeley counterprotest. A myriad of signs proclaimed Berkeley’s rejection of hate and white supremacy and expressed support for immigrants, people of color and other targets of Trumpian rage. But among the peaceful demonstrators were dozens of black-clad, masked Antifa, a frightening sight as they marched in a menacing phalanx.

They claim they were there to defend themselves and others. But, commonly, there is no violence at protests when they don’t appear, and when they do, their macho warrior posturing provokes violence even when they don’t actually initiate it.

At Berkeley, a hundred members of Antifa crossed police barriers to assault the Trump supporters. Not surprisingly, the violence of this handful won more media attention than the message of the peaceful thousands.

Their assault was profoundly misguided. Violent efforts to suppress or expel white supremacists can only weaken and harm the movement to defend democracy.

The rightists need to be tolerated — and, indeed, should have been protected — not because their speech is innocuous, but because suppression is worse.

First, attacking them changes the subject of contention from their racism to our tactics. Do we want people discussing the right’s pathetic defense of Confederate heroes — or our violence against them?

Second, violence feeds the Fox News and Breitbart storyline that progressives are enemies of freedom. Just as Weathermen helped the GOP convince middle America that opposition to the Vietnam War was an unpatriotic fringe activity, the Antifa antics promote the falsehood that leftist violence is the main problem, not resurgent white supremacy.

Third, Antifa confrontations — even their combative appearance — discourage participation by masses of people who don’t want to be caught in a riot. The Women’s Marches following Trump’s inauguration had a giant impact because millions took peacefully to the streets. That impact would have been completely undercut had a handful of militants wreaked acts of violence in the name of “anti-fascism.”

Fourth, if it is deemed acceptable in Berkeley that local police need not protect those whose views are deemed hateful and repugnant, that same principle will cut against us elsewhere in America and will be said to justify ignoring violence against progressive speakers, particularly in places where, for example, local politicians claim Black Lives Matter is a “hate” group with a violent anti-police ideology.

Finally, if political violence becomes the norm, the fighting won’t be limited to fists, sticks and Mace. After all, which side has the guns?

Antifa thinks only of its immediate satisfaction in expressing anger. But politics is not just about self-expression. It is about effecting change, and this requires influencing millions of people who don’t presently agree with us. The political theater of Berkeley is playing on the larger stage of America, where Antifa’s militant posturing and self-indulgent violence does grave damage.

However they may think of themselves, Antifa is actually just what the right-wing ordered. Its tactics have no place in the struggle to defend American democracy.

Mitchell Zimmerman is a former UC Berkeley law student and frequently speaks at Berkeley intellectual property programs.