After the recent parade of hate in Charlottesville, it's only natural that local leaders across the country want to avoid demonstrations by any faction within the so-called "alt-right." That includes leaders in San Francisco, where just such a demonstration has been planned on federal parkland at the city's northern tip.

Federal authorities have approved the event, and House Minority Leader Nancy Pelosi is just one of many local political leaders to object to their decision. And she gave an especially strange answer when asked how protesters' right to assembly and free speech can be respected if they're banned from protesting in San Francisco.

"The Constitution does not say that a person can yell 'wolf' in a crowded theater," Pelosi told a reporter. "If you are endangering people, you don't have a constitutional right to do that."

We can all chuckle at Pelosi's garbled formulation (it's supposed to be "fire," of course, not "wolf"), but the misuse of this argument is no laughing matter. As capable commentators have pointed out online, many people may be unaware that the Supreme Court only briefly adopted the line of thinking represented by the "crowded theater" phrase. And thanks in part to the catastrophic consequences this had on freedom of speech, the court has long since discarded it as far too restrictive of free speech.

Yes, it may literally be true that you can be arrested for falsely shouting fire in a crowded theater. But what sort of political speech actually takes on a character parallel to that example?

When Justice Oliver Wendell Holmes penned the phrase about shouting fire in the theater in 1919, he was making exactly the same argument as Pelosi and others do today. Certain forms of speech, in Holmes' words, "have all the effect of force." In other words, some messages, even when delivered without violence, are themselves violence and can thus be criminalized.

Despite its rejection by the courts, this view has gained currency on the political Left lately. It forms the basis of the completely unfounded and wrong idea that hate speech is not protected by the First Amendment. And you can appreciate how terrible an idea this is by looking back to see what the suppression of speech under the Holmes-Pelosi theory actually looks like.

What was the "shouting of fire" that Holmes thought government was permitted to suppress in his day? Speech and articles opposing the draft during World War I. In his view, Congress was justified in criminalizing anti-draft speeches, articles, leaflets, and the like, because they threatened a sort of societal panic that could obstruct the war effort.

"[I]f an actual obstruction of the recruiting service were proved" as a result of such speeches, he wrote, "liability for words that produced that effect might be enforced." Yet, he added that even if an anti-war message is unsuccessful and fails to obstruct the draft, the intention alone is proof of criminal speech.

So, there is some irony that this terrible argument, now swiftly upon the tongues of progressives hoping to ban messages they don't like, was created specifically as a justification for jailing anti-war activists and leftists in particular.

It led directly to the 1919 conviction and 10-year sentence of Eugene V. Debs, whose crime had been simply giving an anti-war speech that urged "continuous, active, and public opposition to the war, through demonstrations, mass petitions, and all other means within our power."

No rational person would dream of defending Holmes' argument in 2017. After all, this is America. We have a First Amendment, and dissent is supposed to be patriotic.

But an awful lot of people don't think things through. And even upon recognizing the origins of the "shout fire" argument, they may well argue that anti-war messages are good, but anti-Semitic messages are bad.

And that's true, but this is where they lose control of the argument. If the courts allow one opinion to be deemed criminal, then the Congress and all 50 state legislatures will pounce immediately with their own ideas about which others should also be illegal. And even if our progressive friends approve when California bans pro-life protests as somehow hateful or sexist, what sort of speech codes will be written in Texas, Utah, or South Carolina? What will Congress have to say about war protesters when the next conflict arises?

Most importantly: Should any legislature or president ever have such power, to imprison people for stating opinions? The founders of this nation certainly didn't think so, and that's why they put the First Amendment in the Bill of Rights.

Justice Holmes eventually backed away from his own "shouting fire" standard for free speech. And in the time since, the Supreme Court has read the First Amendment in a far more consistent way that protects as much freedom as possible. Recognizing that the Founding Fathers deliberately took it out of the legislature's hands to decide what good and bad political speech looks like, the court has made clear that the only sort of speech that can land you in jail is the sort that is " directed to inciting or producing imminent lawless action and is likely to incite or produce such action."

Note the great care taken in this phrase. To run afoul of the law with one's tongue, one must not only intentionally encourage lawlessness, but encourage it with an actual likelihood of success in causing it.

Moreover, the Supreme Court has repeatedly prevented governments at all levels from suppressing lawful protests through the abuse of the permitting process, which is precisely what Pelosi seemed to recommend.

All of the freedoms in the Bill of Rights come with downsides. But the upsides are much greater. The near-complete freedom of the First Amendment is designed specifically to protect unpopular opinions, unpopular protests, unpopular religions, and unpopular journalists, because that which is popular doesn't require protection.

If the idea that opinions equal actual violence ever gains traction, then the First Amendment will be meaningless, and this society will no longer be free for anyone.