Well, shucks, I can't help but toss my two-cents in this one.

The foundation of exremism is nothing more or less than human nature. The desire that some folks have to tell other folks that they have to live their lives precisely in the way that they, the extremists, say. Why? ah-ha! Because God told me! I know what's good for you better than you do! And this starts the whole process. "God" becomes merely a very large lever to force others to subjugate their commonsense to your directives.

It runs in the same vein as lust for wealth, influence or other means to leverage power or control over others.

Well I think anyway

CLB