I'm arguing that what makes a troll is not criticism or even offence, but malice: those who bully are hoping to cause pain, and revel in it.
This, in turn, is often because of their own anguish, anxiety or discomfort. They seek to diminish their own pain with pleasure in others'. A sample:
Despite the rhetoric - my own and others - trolls are not monsters. They are, in fact, boringly human. Indeed, this fact is often behind their desire to hurt: a heightened feeling of their own ordinariness, smallness, ugliness. Malice rarely comes from confidence, joy, pride; from pleasure in oneself. Instead, it is born of pain.
This is either because one sees one's own psyche and achievements as pitiable and petty, or because they seem so next to a hated other's.
Often this is because of rivalry - the reporter trolling the up-and-coming columnist, for example. But it can also be the absurd envy of the pop culture consumer, who is oddly diminished by the glamour, fame and income of a celebrity who is a stranger to them.
In each case, the common drive is revenge: this somebody highlights my shortcomings, and causes me pain, and so I will seek my pound of electronic flesh. It is a pathetic but common lurch at equilibrium; an animal protecting itself.(Image: Vampire Explored)