That's a caricature. A lot of the perpetrators, like in 9/11, are highly educated and even westernized people, not some backwater goat herders believing such BS.
They could be attracted to those tactics as a mean of compensating for personal issues etc (same way weirdos shoots up a school or a cinema elsewhere), but the political element is involved too.
The fundamendalist is not someone who believes naively such things (most devout village folks are peaceful and pragmatic and could not care less), but rather someone who "goes back" into believing such things (and even has self-doubt he tries to shake by action etc).
I am fully aware of this, I said so in other comment. https://news.ycombinator.com/item?id=10564189 The mistake you are making here is the idea that otherwise intelligent and educated people cannot believe crazy things. Just look at the Christian nutjobs.