People get downvoted by others who disagree with them or just don't like what they said. The same comment would get upvoted in one community and downvoted in another.
I don't think sorting a user's comments by controversal is going to get you the data points you think about.
I still think it would be a cool feature, mostly for the novelty of it, but I do not believe it will be anywhere close to a measure of how inflammatory a user is.