"It's not about people, jokes, and #brands. It's about information, about news and pictures and stories."
Look at every other mass communication system, ever. They all have had to deal with noise. Online site owners have evolved some things that work pretty well, like Slashdot's moderation system with metamoderation, voting schemes, "like" buttons, etc. More than 20 years ago usenet news had cancelmoose. Offline we have long had people like newspaper editors, publishers, standards and practices teams, and even government censors.
Either publishers find a way to deal with spammers, trolls, and griefers; or readers abandon them once the signal-to-noise ratio gets too low as they collapse under the weight of carrying terabytes of gibberish and spam. Frankly I'm surprised Twitter hasn't offered this kind of solution sooner.