I think people seek religion when their world fails them in some way. Those born in that stay either haven't done the work to critically review their faith or they know something isn't quite right but stay due to family, friends, and a sense of community.
Instead of doing the difficult work of re-engineering one's life when something doesn't work, they turn to the easy solution of 'faith' - faith that God will fix everything for you. And that sometime in the future, typically after you've died, if you pass some imaginary trial judgment, you will be gifted with eternal life in paradise.
Anything fundamentalist or extremist is worrisome. It only takes one nut job in the right position of power within a religion for it to become fundamentalist or extremist.
To paraphrase Christopher Hitchens on Islam:
"Islam claims to be the Total Solution. The word 'total' is the first 5 letters of the word totalitarian."