Most people would agree a troll is someone who exists in an internet community solely to cause trouble and make people angry.

Sometimes it's obvious. If a thread in /anime/ is titled "Gook Cartoons are for Little Girls and Social Deviants", it's pretty clear this is a troll, because this board was intended for fans of the genre and they shouldn't have to defend what they enjoy in such a place.

In a board like /politics/ however, we can't ever really call anyone a troll. Most posts have the potential to make someone angry or seem ignorant thanks to the natural human instinct to filter out information that contradicts our world view.

When it comes to religion, every post will be a troll. Any discussion is impossible when dealing with something so tied into self-identity. Walking up to someone and saying "there is no god" or "you will go to hell when you die" is no different than saying "you're a fool and a liar, you've wasted your life in a fantasy world, and your grandfathers corpse is being eaten my maggots" or "you're a disgusting evil person and deserve to suffer while I watch and laugh and eat popcorn". All statements are as true and valid for someone as the color of the ocean but are still deeply offensive and sure to tear people apart and drive some to see red and then black and wake up next to a bloody hatchet. But deleting anyone of them is censorship.

How can we say someone is a troll without knowing his intentions?