Reddit employs an automoderator bot that supports a lot of different types of customization. Each subreddit may have a completely different bot configuration.

Reddit employs an automoderator bot that supports a lot of different types of customization. Each subreddit may have a completely different bot configuration. In the same context, you would think that the asshole/quality spiral (love this description, by the way) could be managed by a combination of moderation bots/humans and (especially) the voting system, but when a sub gets big (say 70k users), it's quite often the assholes who are most vocal and cause the most trouble. With that amount of users, there will be a certain amount of "brigading" and a certain group of users who will play along with the griefers for fun. It's been mentioned above, but a user base can reach a "tipping point" where it becomes impossible to manage with a a small amount of moderators, a bot and a voting system. Something will eventually give. I've seen all this play out numerous times and experienced it first-hand.