Discussions related to politics or religion are available on an opt-in and opt-out basis only (opt-out by default).
Sounds like a good compromise to me.
As forums evolve and people come to know one another, restricting them to specific topics only becomes like herding cats. We are social animals and we like to chit-chat and to argue. Politics and religion are two hot-button items. I've been on forums where they've tried to forbid those topics, and it always winds up causing more dissension than it prevents. The smart forums create sandboxes where those discussions can take place, so that those who are also interested in them have a place to vent with people they know (whether they agree with them or not
One of the forums I'm on broke up the political discussions into two rooms, Red (conservative) and Blue (progressive/liberal). Anyone can read the posts in either room, but if you post in one room, you're forbidden from posting in the other room for 45 days. You also can't quote or refer to specific posts in the other room. This cuts down on trolling and flame wars, and since news topics change so quickly, the 45-day time limit gives topics a chance to cool down (not to mention, if you're used to posting in a political forum, it's almost like going through withdrawal to not post for 45 days just to be able to change rooms.