From what I understand, upvotes signify "this adds to the conversation" and downvotes signify "this subtracts from the conversation" -- it's a stronger sentiment than disagreement, but weaker than trolling or abuse (which is what flags are for.)

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