Disenfranchised youths and teenagers in general are very impressionable. This makes them highly sought after as 'marks' for radicalization. Whether they are already believers or whether they re-discover their religion is besides the point, the whole thing has about as much to do with religion as the war on drugs has to do with curing addiction. It's just a means to an end, a handle to get a grip on these people so they will do what they're told to do. The fact that religion pre-selects for people who have a very hard time separating fact from fiction most likely also has nothing to do with it because even atheists commit terrorist acts.

The puppeteers are the ones that matter, the 'terrorists' are for the most part tools in the hands of masters at playing them believing they are making the world a better place (and how wrong they are).

I make no distinction between idiots of any plumage, be they muslim, Christians, atheists or something else, organized or acting alone. They're a plague on society and should be dealt with, preferably long before they can become a problem in such a way that becoming a problem never even enters their minds because they're too busy living and appreciating life.