Here's a couple regarding atheism, Eric Hoffer would have agreed with your take on Atheism:
The atheist is a religious person. He believes in atheism as though it were a new religion. He is an atheist with devoutness and unction. According to Renan, 'The day after that on which the world should no longer believe in God, atheists would be the wretchedest of all men.
The opposite of the religious fanatic is not the fanatical atheist but the gentle cynic who cares not whether there is a God or not. The atheist is a religious person. He believes in atheism as though it were a new religion.
You should read the book, he also takes on one of your favorite subjects: intellectuals.
Just off the top of my head, people that grew up in a Judeo-Christian society yet still became murdering assholes, and this is despite the fact that Americans are much less inclined to become radicalized due to a number of factors addressed in the book.
Adam Lanza
Dylan Rooff
Ted Kacynski
Timothy McVeigh
Whoever the Heaven's Gate cult leader was.
Jim Jones
Eric Harris & Dylan Kleibold
Fanaticism, radicalization, mass movement, whatever you want to call it; it comes in many flavors and neither the absence nor presence of religion is essential. Islam may be a precursor of sorts, but Islam alone cannot convince a 20-something to strap a bomb to their chest, there is much more psychology involved and there are members of every religion that under the right circumstances could be convinced to do the same.