My understanding is there are two phenomena here in play: forum rules and aggregate forum political culture.
Forum rules will generally discourage any political commentary that doesn't fit extremely unambiguously into the curiosity mould (because observation of how political discourse goes on other sites leads to some pretty strong prior beliefs that both assertions and "just asking questions" can create a climate that rapidly degenerates into useless flamewar). By the rules, plenty of discourse in the political space should probably be discouraged; it's default thin ice.
But moderators focus on threads that leave a big flag / downvote wake, and there aren't very many moderators (one?). So in general, a subset of commentary will have the "eye of Sauron" drawn upon it, and that's the subset that the average reader with more than N-hundred karma finds objectionable.
Forum rules will generally discourage any political commentary that doesn't fit extremely unambiguously into the curiosity mould (because observation of how political discourse goes on other sites leads to some pretty strong prior beliefs that both assertions and "just asking questions" can create a climate that rapidly degenerates into useless flamewar). By the rules, plenty of discourse in the political space should probably be discouraged; it's default thin ice.
But moderators focus on threads that leave a big flag / downvote wake, and there aren't very many moderators (one?). So in general, a subset of commentary will have the "eye of Sauron" drawn upon it, and that's the subset that the average reader with more than N-hundred karma finds objectionable.