Its because as people get “more religous” they tend to be more black and white. we have trouble seeing the gray .
I’ll give you an example.
I concede that for Israel Trump is better than Hillary would have been. but I add that I don’t think Hillary would have been HORRIBLE it wouldn’t have meant the end of Israel, and there are other factors that matter too.
The response I usually get to he above is not disagreement with the actual sentiment expressed rather something along the lines of “Oh so you hate Israel” or “Oh so Israel is not important”
Its a lot easier to say “well Trump is better for ISrael therefore anyone who is not Trump is an evil antisemite who wants to kill all Jews”, than to take a more nuanced approach .
A secondary reason is we as a community suffer very much from groupthink