When people use their free time to cultivate bad feeling, whether it's around the water-cooler or around the blogs, one has to wonder what they're getting out of it. I suspect it's just emotional stimulation within a life with not enough oomph in it.
Like children who aren't getting enough positive attention to suit them, they act in inappropriate ways to get ANY attention AT ALL. Children require attention, but when that drive continues too long it becomes pathological -- adults should be able to self-teach and self-amuse. We should be able to find our niche of like-minded people, friends with similar interests, and venues where debate is fruitful.
Debate is GOOD. This is how concepts are refined and fine-points clarified. Forums are designed for this.
Trolling seems to be the urge to debate that hasn't quite reached its majority; it still has some growing-up to do. A social milieu is being deliberately disrupted, similar to one gang invading the turf of another. The points of view cannot constructively cooperate. There's not a chance in hell of convincing the adversary, so the attempt to do so is a waste of time and energy. Nevertheless, MUCH energy and time are lavished in this activity. Do the words "get a life!" leap to mind with others besides myself? ;-)