I definitely agree, a lot of the meanness of these sites is facilitated by their structure. Once something gets wide exposure it becomes an easy target for vitriol and microblogging sites like tumblr and twitter are all about getting some item wide exposure and promoting it and promoting it to as many people as possible as its marketing strategy. It's really the same if you look on Reddit -- once a subreddit becomes a 'default', meaning you're automatically subscribed to it upon making an account, that subreddit becomes a cesspool, while smaller subreddits devoted to one thing are much, much better, as long as they have decent mods. Hell, the same thing happens with YouTube because of the suggested videos setup. It makes more money to give people a 2 Minute Hate. People get heated and want to argue and they keep coming back to the site, only to see more ads!