But this passage – in a footnote to volume 1 of The Open Society and Its Enemies – isn’t his clearest, and it’s been grossly abused by both the far left and the far right.

The far right reads it and says: “See? Even tolerance itself is intolerant! So let’s persecute whomever we please. Unlike so‐​called ‘tolerant’ people, we’re not being hypocrites!”

And by this thin, almost imperceptible difference, they imagine themselves the moral superiors.

This though is a gross misreading of Popper. The liberal society that defends itself in the face of deadly violence is in no way comparable to the groups that would destroy it.

That’s because to preserve itself, a liberal society first tries things like rational thought, open debate, voting, and a system of laws that allow even odious beliefs to be explored and held without fear of persecution. Liberals reach for violence only as a last resort, if ever, and only when the preferable methods have failed. We use violence only rarely and only defensively, with the aim of returning to a more civilized mode of existence as soon as we possibly can.

For illiberal groups, violence is not the last resort. It is the first resort, or nearly so. Popper’s paradox notwithstanding, there is a world of moral difference here.

Meanwhile many on the far left have also misread Popper, again to no good ends. As stated here, and not altogether fairly, the paradox runs:

A tolerant society should be tolerant by default, With one exception: it should not tolerate intolerance itself.

But Popper never believed anything like this. Rather, he wrote: