It seems to me that HN is relatively neutral in terms of your opinion; People here seem to avoid the vice of downvoting based simply on a difference of opinion, at least in my experience. The community generally seems to award karma based on how thoughtful and carefully-constructed your comments are. I have one one occasion been downvoted into oblivion for politely and carefully expressing an opinion that is generally morally unpalatable, but someone came to my defence and I eventually ended up with a small amount of positive karma for the comment.
I think the easiest rule of thumb is to try and be the opposite of cable news. The calmer and more dispassionate your tone, the more detailed and precise you are in your reasoning, the more carefully you reference reliable sources, the better your chances of being strongly upvoted.