of fundamentalism is really an essential point.
I think it corresponds with the populist political reaction to a society that is not functioning well and it may be symptomatic of that. When people, in significant numbers are not doing well financially or otherwise that, to me, also provides a fertile ground for simplistic or religious views that border on, and descend into some sort of authoritarian fascism.
When you consider that education and critical thinking play into this, it is not hard to imagine the how and why of this. Let's say you have a liberal education and have learned to think somewhat critically. You may also have quite a bite of reading behind you. In that case, you have opened your mind to more complex issues that may still be overwhelmingly complex, but the gradual exposure over time has made that less daunting and mysterious to you. You can have a good sense for it and know where and how to look for more information.
Now, let's consider that you have only had a basic education up to High School and also little exposure or interest in reading anything outside of some simple interests at best. In that case, when things get bad, (and I am generalizing here) confusing, chaotic, frightening, then an offer of "it's all here in this book and it is certain truth" is going to be far more appealing and the politics that get attached to that will follow in suit. without critical thinking, that point of view can spread easily, especially for those in environments where it has been extant in one way or another traditionally.
We don't really face a problem of religion, per se, (many rights movements have been connected with religious ideas or rights based on that) but, as with any style of religious belief, it is fundamentalism that is a clear and present danger. Separating the two makes sense when it comes to our alliances in resisting fundamentalism, fascism and even oligarchy because none of those categories are compatible with, or even tolerant of, true democracy which is pluralistic, tolerant and opens a wide, sectarian umbrella for its citizens. It is the common will for the common good and even provides due support to our commons in all forms.