I have seen this come up with politics in foums, I have been involved in forums for 15 years.
Either ban it outright or do this, keep it in one section. Be strict, say in order to maintain neutrality, or not offend, either off limits (best) or kept strictly in one area. You are going to have to be vigilant without being too censoring. This destroyed one guys forum and it WAS number one in the world for its niche. The guy got too heavy handed about censorship so a competitior started another, less censored BB....He let emotions get in the way of just having a policy and sticking with it.
Tough one and you are wise to understand that it has potential to go south. You also might want to bring in a couple of mods so all the heat doesn't come your way when it comes to moderating.
Post the new rule(s) and then respectfully ask for feedback while announcing the new moderator(s) may be the way to go.
Good luck!
+ Reach out to the one of the nutcases and tell them that you feel that, as a warrior for Jesus Christ, religious topics should be placed in their own special place, and could he please moderate that forum. For baby Jesus?
Use the power of insanity for your own benefit.
If the sub-forum gets too big, delete it periodically and claim that you were "hacked by the Jews again".