On the Christian forum I run, we don't allow people to proselytize other religions. We allow discussions of other religions, but the OP cannot start a thread in hopes of trying to sway people away from Christianity.
The only topics I won't allow are those who personally attack others based on their religion, race, sexual orientation, gender identity, etc. Pretty much everything else is on the plate to discuss, as long as it's all in good faith and everyone can behave.
I wouldn't allow my users to discuss on sex, weapon, alcohol, drugs, and all topics that are banned by adsense. On my general discussion forums there are topics on religion and politics, I think these are ok as long as people do not make personal remark without any proof.
I allow debate, even politics and religion, until it becomes toxic and abusive, then I take action.
What I don't allow is violations to the rules. Discrimination and racism is a rule violation. If you make a post favoring that soret of behavior as if you're just debating, in my eyes, you're violating the rules and that's when I'll put a stop to it.
