Comment by godelski

Also note that votes don't just mean agree/disagree. I frequently upvote comments I disagree with and downvote comments I agree with. The votes place the comments in the discussion ranking so plenty of people vote this way.

One example of this is I might like a conversation that's responding to a comment I don't like. But it's a common misunderstanding so I want the conversation to be boosted. Therefore I upvote the comment I disagree with because it's parent to the comments I want to be more visible.

I don't think I'm the only one that does this on HN. And I think doing this can help reduce the repeated comments. In the above example an early common misconception might get downvoted, not seen by others, and then repeated by some, where it can then rise because it's seen by a different subset.

Anyways, I don't think people should vote strictly on agree/disagree