Senator Ed Markey went on CNN earlier this month and appeared to break major news in the investigation of the Trump campaign’s ties with Russia. “There are very strong allegations the Russians had relationships with people inside of the Trump campaign,” the Massachusetts Democrat said. “In fact, subpoenas have now been issued in northern Virginia with regard to General Flynn and General Flynn’s associates. A grand jury has been empaneled up in New York.” While it was known that federal prosecutors in Virginia had subpoenaed associates of Michael Flynn, Trump’s former national security advisor, the grand jury investigation was news to political reporters who were watching. Fake news, it turned out.

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Markey’s mistake was the latest and perhaps most prominent example of the rise of conspiracy-mongering on the left, prompting some to worry that liberals are heading into the same fever swamps that have swallowed up the Republican Party. “Mensch and The Palmer Report are part of a disturbing emerging trend,” the New Republic’s Sarah Jones wrote after the Markey incident. “Liberals desperate to believe that the right conspiracy will take down Donald Trump promote their own purveyors of fake news.”

The left ought to be concerned about this trend, but some have gone so far as to apply a false equivalence to conspiracy-mongering. The Russia theories haven’t taken hold among Democrats in nearly the same way that countless right-wing theories—like those about Barack Obama or Seth Rich—have gripped the Republican imagination. That’s because the two parties are fundamentally different: Only one of them acts responsibly when faced with politically convenient, but obviously fantastic, stories.

Less well known is the paradox of tolerance: Unlimited tolerance must lead to the disappearance of tolerance. If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them.

In this formulation, I do not imply, for instance, that we should always suppress the utterance of intolerant philosophies; as long as we can counter them by rational argument and keep them in check by public opinion, suppression would certainly be unwise. But we should claim the right to suppress them if necessary even by force; for it may easily turn out that they are not prepared to meet us on the level of rational argument, but begin by denouncing all argument; they may forbid their followers to listen to rational argument, because it is deceptive, and teach them to answer arguments by the use of their fists or pistols.

We should therefore claim, in the name of tolerance, the right not to tolerate the intolerant. We should claim that any movement preaching intolerance places itself outside the law, and we should consider incitement to intolerance and persecution as criminal, in the same way as we should consider incitement to murder, or to kidnapping, or to the revival of the slave trade, as criminal.