I'm trying to empathise with them... I get why people become radicals of other kinds... but saying no music, no sex, live by the book, behead those who disagree... what part of that makes people think "I want to get into this, this sounds fun"?
The Arab world has valid grievances, which motivated 9-11 for example, but there's more to it than that.
Blowback season 4 has great coverage on how the US propped up far right Islamic movements, leading to the Taliban among other groups. These movements aren’t often organic in origin. People aren’t naturally predisposed toward this path. So much of it has been directed and supported by foreign powers for their ambitions.