Both anonymity and scale reduce what Robert Axelrod calls "the shadow of the future"—the sense that our current actions will have consequences down the road.
That provides some options for turning the jerk dial down. One is to make identity valuable: Stack Overflow won't let new users post until they have exhibited enough other behaviors—visiting the site, responding in helpful ways to other posts—to earn the karma for full participation. Another approach is to partition public platforms, thus reducing the incentive to publicly act out. Twitter does this by segmenting its audience: I can rant all I like, but only to the users I can persuade to follow me. Yet another approach is to enlist users in defensive filtering. Amazon sometimes refuses to publish a post, but most of its policing is done by customers who flag offensive reviews and elevate those they find helpful.
Cleaning Up Online Conversation
Clay Shirky on Cleaning Up Online Conversation