First, it's extremely complicated. Second, yeah, it's probably a mixed bag, some probably sincerely believe in their ideology and think that blowing themselves up is a good deed, others are in it for money or other reasons. What has been proven (pretty strongly at this point) is that it's the M.O. of many terrorist organizations to recruit men from poor households... and they tell them after they're dead from the suicide bombings, they'll sustain their families monetarily. To the would-be suicide bombers, this seems like a good rational choice within the reality of their situation: struggling families, living in desolate conditions with not much hope in sight.

The matter of the fact is, a lot of these poor families that are approached by recruits would tell the recruiters to fuck off if they were not in such hopeless conditions.