The problem with the belief isn't that it's religious but that it may be irrational. You'd want to know if someone standing next to you is secretly irrational, insane, or grossly hypocritical. For example, if you're an employer, you may not want to hire someone who doesn't understand the difference between fiction and nonfiction since that could be bad for your business.

Of course, this assumes that so-called religious people are serious about those beliefs and aren't just hypocrites, which is seldom the case. Even if the religions themselves are crazy, most religious people aren't so irrational because they're only pretending to be convinced by the theologies and apologetics. They've been raised in the religion so they go through the motions as adults. Religion is their security blanket.