I have always liked this analogy (from an op-ed on trolling in the New York Times):

Trolling, defined as the act of posting inflammatory, derogatory or provocative messages in public forums, is a problem as old as the Internet itself, although its roots go much farther back. Even in the fourth century B.C., Plato touched upon the subject of anonymity and morality in his parable of the ring of Gyges.

That mythical ring gave its owner the power of invisibility, and Plato observed that even a habitually just man who possessed such a ring would become a thief, knowing that he couldn’t be caught. Morality, Plato argues, comes from full disclosure; without accountability for our actions we would all behave unjustly.

Interesting piece.  But the real problem is the troll who doesn't know it.  I suppose that's why we're here.