Now, one can concede all this and still cobble together a case that Le Pen would have been more dangerous to existing European institutions than Corbyn. She’s a French chauvinist; he’s a lefty internationalist. She wanted France out of the European Union; Britain has already taken that leap (and a Prime Minister Corbyn would probably make Brexit somewhat softer). She traded in clash-of-civilizations rhetoric about Islamic immigration; he’s fluent in the pieties of multiculturalism.

But some of this amounts to saying that it’s O.K. to elect an extremist with anti-Semitic and authoritarian and even terrorist connections if he or she just takes the official European Union line on immigration and monetary policy. Meanwhile Corbyn’s habits of mind on defense policy — think Chomsky with a dash of Trump — could threaten as much destabilization for NATO as Le Pen threatened for the Continent’s monetary union.

Again, I don’t think it would be a better world if Corbyn were being met with Le Pen-level fear and loathing. The entire populist phenomenon, left and right, is happening because our establishment is in need of serious unsettlement, and that can’t happen unless movements and ideas with extreme or disreputable associations are allowed into the conversation…

Nonetheless — in allowing the extremes in, we should not be blind to where their worst tendencies can lead. No such blindness is likely where the right’s populists are concerned, since the entire media-intellectual-academic complex of the West has its fascist radar set to “high.”