This is a pretty big tangent, but I fairly strongly disagree with pg on this. The fact that upvotes and downvotes are not treated symmetrically seems to imply

This is a pretty big tangent, but I fairly strongly disagree with pg on this. The fact that upvotes and downvotes are not treated symmetrically seems to imply that they really aren't suitable for merely conveying agreement or disagreement. Somebody's comment shouldn't literally be greyed out, sometimes to the point of being illegible, because a few people disagreed with it. This combination -- using downvotes freely to express disagreement, and hiding or fading out downvoted comments -- is a recipe for groupthink. It's very nearly a form of censoring comments that are maybe contentious but in no way inflammatory or off-topic or poorly written.