It's funny, because the reasoning (from what I understand) for subreddits instead of tags was that subreddits create distinct communities. While this is true, cases like FUU comics being in every subreddit point to subreddits as failing to contain their communties. With an additive tag system (Show me posts tagged "Minecraft") or the current system, those posts show up anyway. With a subtractive tag system (For the love of god, no more "FUUU"), they wouldn't show up.

Either way, I agree with you on FUU comics. They became so pervasive I just gave up and deleted my account.