I would guess that they don’t actually *read* the Bible much. Most work off of bad-faith (literally and figuratively) interpretations they get second hand. The ones who actually do read, then, go look in the Bible for further proof of their pre-existing worldview. Looks the same in the end.
I think that they also do that, but I think we are giving them way too much credit when we think that they would be better if they actually read the Bible. I really do think that the truth is that they are able to be all kinds of evil despite many of them reading the bible constantly.
I think a lot of it also happens from being in relatively isolated communities that will reinforce that they are the good guys at war with "the world" out there which is evil.
The apocalyptic stuff is dangerous fanfic at this point