My point is that a comment filtering system is consciously based on the identification and exclusion of a group, which we'll call the out group. Of course it's limits will be debatable, just as the definition of spam is debatable.

If what you're excluding is political speech of a sort, then someone is going to be able to accuse the system of censorship, no matter where the line is drawn. It's inherent in the system's goals.

Personally, I think that's a point where any system is going to be rightfully challenged and examined critically, but I think it's still worth doing on a greater good basis. Spam filtering works, it makes my inbox a more tolerable place. It's a good idea to extend it to other types of crappy speech that makes other peoples' lives worse.