What is pulling Western-born boys, a surprising number of them converts from other religions, to the grisly banner of Islamic State? Surely a lot of the attraction has to do with the pitiless confidence that characterizes all totalitarian movements. The Salafists, like the Bolsheviks and the Nazis before them, promise a new age. Everything will be swept away: laws and nations and customs. An ideal so abstract as to be apparently unattainable will somehow be realized.

Some young men, in every age and nation, are attracted by unachievable purity. They like the appeal of trial rather comfort, of struggle rather than prosperity. They can hardly help contrasting the apocalyptic certainty of Islamic State with the self-doubt of the West.