Trolls do nothing other than derail and disrupt discussions for the amusement of an individual. It's a selfish and self-centered act of provocation that has no place in civilized discourse anywhere. I can certainly say that some of the troll-free debates here have actually changed my mind on a few things. If a troll wants some entertainment, it can watch something on Netflix.
No debates whatsoever should be banned under any circumstances from anywhere. Why should they? For what benefit would they be? Censorship never does anyone any good, and always be weary of those who sell censorship like clergymen selling you the afterlife for obeying them. It's time we realize that as a society.