Forgive me if this was ever tried, but what if one more rule, this time regarding religion and politics, two topics which everyone here is always divided in, was made?
At another forum I frequent, a "No religion/politics" rule was made after tons of people kept arguing about both. It actually has worked quite well. All people who didn't comply with that rule and made a thread about either topic was told that it was against the rules to make a topic regarding it and the thread would then be locked or deleted. If people started talking about it in an existing topic, they'd be told to shape up and refrain from continuing. If no one listened, the thread would be closed after awhile.
...If no one thinks this is a good idea for the forum, I'll completely understand, and just, uh, crawl back into my little hole until I can think of another thread that gets a lot of attention.