Religious questions are much easier than political questions, and can be answered with much more certainty. Political questions are also detrimental to sane discussion because they often rest upon (disguised) moral questions, which encourage tribalism and are harder still to resolve, if they can be resolved at all.

Religious opinions are divisive, we took our side, and don't seem to be considered very highly by those who took the other.

I don't mind closing the community to believers, in first approximation their ideas are worthless. But I wouldn't extend that to liberals, libertarians, conservatives, environmentalists, anarchists, etc.

I can't think of any other topic beyond religion and politics where it's commonly expected that everyone has a position - some people can have strong and conflicting opinions on say parenting styles or whether Esperanto is a real language or interpretations of quantum mechanics or operating systems or whether Batman could beat Superman, but they don't go around saying "Oh yeah he disagrees with me because he's a yellowist" or something like that.