The local blogosphere was destroyed by an infestation of Trolls. This week's Economist had an interesting article on the phenomenon.
It is the anonymity that the internet offers that brings out the base characteristics of people. There is a parallel with real life, I think it is the relative anonymity of an existence in a large city that brings out the worst in people. Crime always seem far worse in cities than in smaller communities.
When people know who everyone else is then that knowledge acts as a check on behaviour. A social check of sorts. There will always be a few incorrigible elements or black sheep but most would think twice if they knew that word would get round soon enough and their reputations and those of their family were at stake.