They join because they believe strongly in bullshit religious propaganda and don't believe in human rights.

Well, it's not so much "They join" so much as "They are members".

And it's not so much "because they believe" so much as "They believe because."

It's rare for terrorist sects to win converts over from moderate backgrounds, if my understanding is accurate. Overwhelmingly, people involved in the most radical religious groups grow up culturally immersed in theology, violence and strife, and so their belief in the ideals of the group and their membership in the group are often sort of a chicken-and-egg situation.

It's extraordinarily hard to find a north american musilm who wants to blow everyone up, even though there are some examples of imams in the West preaching a theology just as conservative as any jihadists'.

The other necessary elements are not present here; violence and strife. If a kid grows up hearing from their religious community that the society around them is cursed by God and must be cleansed by the faithful and it's us vs. everyone, but for the rest of the kid's day they're eating healthy food and living in a nice house and maybe even going skateboarding with a group that includes a couple of basically chill white kids from down the road, that extreme theology is just gonna turn into a background litany of rules that he doesn't bother to live up to and has to cultivate some cognitive dissonance about, just like any ultra-conservative christian does when his preacher tells him it's the end times but he stays invested in long-term mutual funds anyway.

It's only in an environment of hostility and besiegedness (such as exists in some parts of the Middle East, and to a lesser extent for Muslims in France, where popular opinon and government policy have a pretty specific anti-Islam thing going on) that those extreme viewpoints ever get a chance to really become relevant in people's lives. Muslims in America just don't have much to galvanize against, so that chicken-and-egg cycle which happens in extreme factions doesn't really ever get up to the point of self-perpetuating.