I would even for you if the pop was like this!
Well being trolled, by a troll will surely lower the population far more then a troll being banned who will inevitably comes back for the high of trolling.
I mean his whole point of doing what he did was in make me feel small relative to himself, or rather to ruin any sort of enjoyment that I was having and sort of take that and add it to his own. In layman's terms he was bullying me, making me feel small though his use of power, and as a result to make himself feel big, strong and powerful.
That sort behavior will lead to more people being upset and not wanting to play then just him who will get back to being a douche (hopefully within the rules) after the ban expires, otherwise that rush from the blatant exertion of power (which is part of human nature) will encourage him to continue the behavior... Trust me I know.
There is also the notion of justice to consider, but it concerns me so I wouldn't take that into consideration.