I completely disagree, if you introduce licenses for content providers you suddenly raise the barrier of entry. In one fell swoop you'll push yet more communities underground and inhibit those little sparks of creative which begin an explosion.
Your sentiment I do agree with and we should think of ways to introduce accountability or self policing of some kind. It is simply almost impossible to remove negative/pseudo psychotic behaviour from any corner of the web, funnily enough it is a part of freedom we have to manage. Maybe the real answer here is to work with people to mitigate the effects trolls have.
MATH AND ALCOHOL DON'T MIX! Please, don't drink and derive. Mathematicians Against Drunk Deriving