I upvote plenty of comments I don't agree with that are well-stated. Make a good case, and my agreement or disagreement doesn't matter. And if there's a comment that I agree with but the writer is being name-calling asshole, I click the down arrow.

Reputation matters not, though those with a better "reputation" probably earned it by generally avoiding trollish behavior.

In general I probably don't fit a lot of the group think that HN is frequently accused of. But if someone makes a well-reasoned case for (say) using Bitcoin to pay my mortgage, I may still think they're nuts while clicking the up button because it makes a positive contribution.

Unfortunately sometimes the first come - first claim creates biases as you might have something very good to say, but I starts with 1, far below the other numbers. Other biases - like the majority not agreeing with you, regardless of your argumentation, are effective as well.

Yet, such voting systems are generally effective.

I would wager that people tend to feel that comments they agree with are of higher quality than ones they disagree with, and as readers of HN are self selected its entirely possible that the entire effect is just an artifact.

I also doesn't make sense to comment along the same lines of another commenter. If my opinion is already expressed in the comments, an upvote makes way more sense imo.