[vivekd]

I think a big part of it is anonymity encourages people to let out the worst aspects of their personality. I think if a forum required people to use their real identities you would see much less objectionable contact (but probably also a lot less interesting ideas)

[pjc50]

No, you'd see (as with youtube and G+) people putting out objectionable content under their own names. While genuinely vulnerable people would tend not to get involved for their own safety.

The problem is one of "lawlessness"; adhoc reprisals from your fellow netizens aren't an improvement.