Not anti religious but I’ve been treated just as poorly wearing Utah gear in a BYU section. Utah fans have had their cars vandalized in the LES parking lot. Fans are fans and you shouldn’t judge a group by the 5% anyway, but if you are looking for a reason to dislike a group, you’ll find one.
Me personally I love most BYU fans as all of my good friends are BYU fans, but I’ve also seen despicable BYU fan behavior, the difference is that the bad language is directed towards Joseph Smith instead of your mother.