Don't think you could find a better definition of troll than the one currently trolling in the space shuttle thread. I agree that we shouldn't be so open-minded that our brains fall out. To me, trolling isn't about the identity/anonymity of the person doing it, but the intention behind it. Many reasonable people remain anonymous in one way or another online.
When the intention is clearly vicious, as the troll over in the space shuttle is, that is where I draw the line. I guess I would use the "no reasonable person" standard, knowing that there are a lot of unreasonable idiots masquerading as reasonable people.