Not sure why politics or anything for that matter should be disallowed. Just make it so everything is allowed, and label the areas differently so people simply use the areas as described.

People who want strictly politics will talk politics in political forums. And people who want gaming with gaming forums. And there may be some cross pollination, but with a big enough user base to accommodate the specified groups, the labels themselves will naturally make people post and upvote relevant content.

No need to moderate anything except site wide rule breaking.