Perhaps this belongs in the bonfire but I'm posting it here because I'm thinking of it more in terms of culture and norms presently.
What way do you define trolls and trolling? Does it have wholly negative connotations or is it something you've either wanted to do yourself or known others to want to do and why?
My two bits, it is something which is wholly negative, usually involving driving people to breaking point and finding this satisfying. In the real world the same behaviour is exhibited by stalkers, certain sorts of predators and bullies. Its not something I'd ever want to do and I'd take being accused of trolling seriously and examine my behaviour (this happened to me once when I was seventeen).
I'm concerned by it because I think the internet does have a shaping influence on people, online norms fast become off line norms and expectations.