“Paradox of Tolerance” is a favorite slogan of censorship advocates. Most often they drop the words in a discussion without elaboration to give the impression they’ve said something profound. Some will mention its connection to Karl Popper. Few will cite his words, since they’re actually opposed to censorship.

The words in question are from a footnote in The Open Society and Its Enemies. The footnote is a bit unclear; Popper was adding a passing thought, not a polished commentary. Here are the words:

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.

An in-depth discussion would clarify what “tolerance” means in this context. It comes at different levels. The most basic form is allowing people the freedom to express their views using their own venues and property. It’s the simple recognition of the right of free speech. A greater level of tolerance is granting people access to an open forum, still without necessarily granting that their views have any value. Beyond that is willingness to engage in a calm discussion of the merits and defects of their views. Popper doesn’t fully clarify what level of tolerance he means.

Popper is saying that there is a right to suppress the “utterance of intolerant philosophies” “if necessary even by force,” but he wraps this in hypotheticals which make it unclear when he’d apply this right. He says that as long as rational argument and public opinion can counter these philosophies, suppression is “unwise.” When it’s permissible is wrapped in what they “may” do. One of those conditions is that their promoters may teach followers “to answer arguments by the use of their fists or pistols.”

This leaves multiple questions open which Popper would doubtless have addressed if he had written an essay on the subject rather than a footnote. His formulation suggests he’d support laws suppressing some viewpoints, such as Nazism. I would disagree with him there; the power to suppress any point of view, when it’s a position and not a direct threat, is too dangerous to grant to a government.

When people toss the phrase “Paradox of Tolerance” around, they’re generally talking about suppressing a much broader range of activity than Popper’s comment would imply. They don’t cite his words because it would be too obvious that they don’t apply. In any case, “Paradox of Tolerance” uttered by itself is a slogan, not an argument. The people who toss it around are trying to get you to believe that their intolerance proves their tolerance. It’s a huge swindle.

For further reading on the subject, see this article by Jason Kuznicki.