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But 'disagreement' is a bit vague. If I use a dwonvote (which isn't for totally inappropriate stuff) it's not merely disagreement, but because the comment has demonstrably false content for instance. I'm not sure what else I'd use it for, just opinion-based disagreement doesn't quite cut it indeed.

I'll try to clarify myself (I thought I was, but apparently not...) by "disagreement" I meant downvoting purely based on not agreeing with the poster's opinions and/or their other comments. (There are people who mass-downvote posters on HN which they want to "punish", sadly...)

If the comment is inflammatory, false or even just misleading, I wouldn't count it under this umbrella.

Yeah I'm in the boat of "people shouldn't use downvotes for differing opinions", but I do downvote things I disagree with when I think they are "in bad faith". This is definitely a vague and subjective metric, but includes things like the demonstrable falsehood you mentioned, as well as stuff like continuing to make the same point while seemingly failing to read or incorporate what their interlocutor is saying.

I guess what I'd say is that most disagreements are honest ones - people coming to different conclusions on subjective things - and that's the kind of disagreement I don't think downvotes should be used for.

I don't downvote all disagreement, and I'll occasionally upvote or vouch a comment I disagree with that I feel has been excessively downvoted.

But I frequently downvote disagreement where it seems to me that the comment also reduces the overall thread quality.