Paul Graham, software entrepreneur, artist, essayist and venture capitalist, writes about online trolls.

…Now when people talk about trolls they usually mean this broader sense of the word. Though in a sense this is historically inaccurate, it is in other ways more accurate, because when someone is being an asshole it’s usually uncertain even in their own mind how much is deliberate. That is arguably one of the defining qualities of an asshole.I think trolling in the broader sense has four causes. The most important is distance. People will say things in anonymous forums that they’d never dare say to someone’s face, just as they’ll do things in cars that they’d never do as pedestrians—like tailgate people, or honk at them, or cut them off.

Trolling tends to be particularly bad in forums related to computers, and I think that’s due to the kind of people you find there. Most of them (myself included) are more comfortable dealing with abstract ideas than with people. Hackers can be abrupt even in person. Put them on an anonymous forum, and the problem gets worse.

The third cause of trolling is incompetence. If you disagree with something, it’s easier to say “you suck” than to figure out and explain exactly what you disagree with. You’re also safe that way from refutation. In this respect trolling is a lot like graffiti. Graffiti happens at the intersection of ambition and incompetence: people want to make their mark on the world, but have no other way to do it than literally making a mark on the world…