People have their own beliefs like Muslim they killed people because they want to go in heaven like what they knows.
So they are killing people just because someone had authored a book in which it is sated that they will get 72 hoors (virgins) if they kill an infidel? This is beyond belief. I don't think that any individual in his normal mental state will fall in to this trap. But still, I don't know why so many people are believing in these fake stories and myths.