Yeah, even if this is very hard to get it perfect, I keep thinking there has to exist a better voting system than what we have. We can do a presumed step in the right direction and evaluate.

- To give an outlet for (dis)agreement: We could have two arrows on each post, one for agree/disagree, the other for 'legitimate post that helps the conversation'. Someone posting wrong info rarely helps the conversation, but also often enough it's an opinion matter and you can disagree while leaving the latter arrow alone. The latter determines sort order (most helpful first); the former is displayed as a fun fact on posts that are deemed helpful (author sees exact counts just like now)

- A system that seems to work better: A local tech site uses a system where you assign a quality level to a post. The short labels are (translated) "flamebait", "irrelevant but well-intentioned", "relevant but well-known", "useful contribution", and "exceptionally useful". Each one has a numerical value, ranging from -1 to +3, and it'll take the median of all votes (with a half-vote bias towards +1 I think, but that's an implementation detail). If your median comes out to -1, it's collapsed by default; at +2 and +3, it gets highlighted. Incorporating opinion into your quality assessment is a problem here, too, but then you might get +0 instead of +1 and not (like on HN) a score of -7. Not just does that feel a lot more fair, the system and its UI also just makes more clear to everyone that you're supposed to objectively score the comments on the mentioned guidelines (it shows a description every time you hover over a vote option)