I think you'd want a comment ranking system that rewarded people for voting according to the thought that went into a comment rather than whether you happen to agree with the comment.
Maybe a two dimensional voting system, one for "quality" and one for "agreement" (literally a 2D voting arrow widget? up-right means "high quality and I agree", down-right means "low quality but I agree", etc).
It would then be pretty simple to see who's "quality" and "agreement" votes don't strongly correlate, as well as who writes quality comments, and weight their votes more heavily.
If you only had 1 dimension voting like everywhere else, then I'm not sure how to do it, but maybe it's possible.