@hightor,
Very interesting discussion. The two different definitions so far are both interesting. They represent different types of trolls with opposite goals. Let's call McGentrix's definition of trolls "abusive trolls" and Hightor's definition "provocative trolls".
Abusive trolls work to enforce social norms. Generally abusive trolls represent a point of view that fits with the social majority. The purpose of the abusive trolls is to punish dissenting opinion. The end goal is a social group with similar points of view.
Provocative trolls serve to rock the boat and to challenge social norms. A provocative troll will look for weaknesses in the prevailing view and poke at them. The purpose of the provocative troll is to upset group think and to challenge the closely held opinion of the social group.
It is a shame that the same word "troll" is used in each of these cases. They are really opposites.