I agree with you completely. I always strive (doesn't mean I never slip up), to only downvote someone if they are not contributing to a discussion. One thing that irks me bad though is when people make emotional claims about complex topics without any references or even logical arguments to back up what they're saying. I really like hearing new opinions, but you cant have a real conversation when the other person is convinced they shouldnt have to convince you.

The most recent thing I changed my opinion on thanks to HN though was smoking - a guy came with studies in his comments, and convinced me there is actually a net monetary benefit govt healthcare systems have from smokers i.e. smokers die younger and the treatment method is shorter than other diseases. Those are the good moments on HN :)