It's obvious now that people will use their anonymity to say whatever is on the top of their heads, but I don't think the creators behind twitter knew how ridiculously vile it could become. Besides that, I have an idea of most twitter messages ranging between pointless and benign. We just tend to notice the horrible ones more...
I've found that discussing almost anything online evolves into standard responses. If someone is typing in a good-mannered way, people assume they're gullible. If someone states something, people will assume they're an arrogant know-it-all. If someone writes in an emotional way, others either respond to it in kind or assume them to be bi-polar freak without self control.
I find the most frustrating people to be those who refuse to consider any other viewpoint than their own. The worst ones are the hypocrits who flat out make no sense when they're caught breaking their own rules, and refuse to reassess the discussion.
Having grown up with instant messaging, chat channels and message boards, I've said some extremely stupid things (like most, if not all people) and facing those things really brings things into perspective.