Some post religious topics solely for the purpose of stirring up conflict (That doesn't necessarily encompass trolling), but others are actually interested in discussing religion in an orderly and respectful fashion. There's no reason to stop people from discussing those sorts of topics if they're all being polite about it. But too often people seem to misinterpret "Well, I think this is wrong, and here's why" statements as rude or disrespectful. They aren't.