If a comment is disagreeable but worthwhile, my preference is to give a substantive response. If a comment is value-subtracting, even if I agree with the sentiment, I'll downvote it (and may take the time to explain the downvote if I think my explanation will be helpful.)
The main attributes I consider to make a comment value-subtracting are:
- substantial factual errors (not just a nitpick, but core to the point)
- gratuitous negativity or unnecessary incivility
- waste of space ("me too", memes or jokes except if they're edw519 caliber, excessive references to irrelevant topics such as mentioning someone else's religion several times in a thread that has nothing to do with that)
- extremely poor reasoning or communication, to the degree that trying to engage substantively becomes difficult
It should be common sense but I suspect not everyone with the ability to downvote has such considerations and the HN guidelines¹ offer very little comment on that.
I'm guessing that mods think that once you've risen above the downvote reputation threshold you must be qualified and should have a good criteria on how to use this newly given privilege.
I'm not trying to tell anyone how to do their job, but maybe it would be useful to add some guidelines for that too (Voting, specifically), I think I like your guidelines.
Eg when I don't know how you perceive the comments in the vicinity of the discussion, it is harder for me to understand your comment's intentions and finer points.
Of course this doesn't apply to peripherical features such as the colour of the header bar.
For the longest time I was confused at seeing down-voted comments because I mentally assumed that downvotes mean "this is a troll comment / this is some kind of abusive comment". Not so.
Also (and I've said this before so apologies for repeating myself!), if downvotes do mean 'disagreement', could we get rid of the graying out of down-voted comments, or maybe just make it an account preference? I'm interested in reading viewpoints that I might not agree with and graying out the comment makes it really hard to do so. It also seems to fit better with the model of "downvote = this comment shouldn't be in the conversation".