People love this kind of fantastical good/evil stuff. Who's good and who's evil depends on what side you're on, of course. Like that Russian book I heard about that's a rewrite of Lord of the Rings from Sauron's perspective.

Look at what games boys and young men so often choose to play. When I was seven I was out in the forests with my friends with fake guns. It was really fun. Then I put down childish things and got into Counter-Strike. I loved playing the terrorists. The AK-47 was just great and the avatars looked pretty cool.

This is kind of off-the-cuff sociological speculation or something, but: religion is a very powerful aesthetic phenomenon. In combination with war, you get a combination of thrills, ecstasy, excitement, danger, meaning, and hope that's hard to beat, for certain personality types.

Look at the ISIS propaganda videos. They're not laying out a rational strategy for improving the world. They're presenting an aesthetic image, a very masculine one, full of cars and guns and desert missions and fighting and stuff. Combined with the pious literalist faith that also has its own appeal. They do offer a hope for a future world, a glorious Islamic caliphate and whatnot, probably the deserts will bloom and peace will reign and Muslim Jesus will rise from the dead.

They say things like "Are you satisfied with your shitty life in suburban London or Paris? Do you like the way people look at you? Do you feel alive? Do you love your life? ...no? Come here. We not only have an exciting virile lifestyle full of action and terrible sublime beauty, but also we are the true messengers of the true prophet and God is on our side."

I will not speak about young people joining ISIS, but I've known people who joined or wanted to join the military strictly to kill. These folks exist. You give them a strong ideological or philosophical reason to kill for and it brings in some of those sitting on the fence. In the case of the US military, I've not known anyone who made it through bootcamp with these attitudes (though I'm sure plenty have). They actively weed out these folks because, while their main mission involves killing, psychopaths aren't usually good soldiers. Groups like ISIS have no qualms in this regard, so these attitudes will survive their equivalent of basic training.

Bullshit. The people who are destroying ancient statues and slaughtering other Muslims didn't sign up for some grand scheme of bringing down the west after a reasoned argument. They signed up because they are violent psychopaths and they were given an avenue to do all of the fucked up things that struck their fancy.