But this explanation is also for young Muslim men that join ISIS.
Yes, this is commonly used a reason ISIS is so easily able to recruit young men. And personally, I think it makes sense, though it's only a small part of the picture.
The other part is that people want to feel like they have a stake in something. A stake in society, a stake in some group. A cause. A way to make your shitty life meaningful.
ISIS offers that, plus the chance to get laid. So they catch a lot of frustrated young men that way and brainwash them.
Looking back at these young white guys getting radicalised, what strikes me more than the sexual frustration is the lack of a group, of a cause. Each minority in america sees itself as part of a new generation pushing towards greater equality, and therein lies their meaning. Women, too, have this sense that they are breaking boundaries and progressing towards some brighter day. You can read any liberal paper and see articles from minority or women authors rallying their peers towards some cause or another - and it's a great thing. It gives life meaning.
But young white men have a total vacuum of that kind of in-built meaning. There's no group identity, no struggle to win, no battles to be fought. Is it any surprise that the angrier and more isolated among them have invented causes to rage against? Whether they are completely fucking meaningless (ethics in games journalism) or utterly terrifying and dangerous (white nationalism), these dudes don't belong anywhere, and they create these groups to belong.
The obvious reply will be 'White guys don't belong anywhere because they belong everywhere - it's their fucking country!' I get that reply, but that's not what it feels like to some useless broke no-talent 19-year old on the ground. He just feels isolated and without meaning. He sees all these minorities rallying for justice and thinks he wishes he had a cause like that. A group to rally with. He's actually envious. And he picks up the torch, finds some friends... and goes off to fight those groups, since the only battle for a white guy in America to fight in his own name is against the loss of status and privilege.