Don't you think that would break the minimalist design? I don't think it would benefit, not to mention it would be a little too opinionated.
I suspect HN's up/down system follows the pattern of simplicity by design and for good reason; the reason being the flexibility to welcome a cognitive diverse audience.
Apparently HN's decline in audience quality over time was expected from the start¹; quality and popularity seem to be inversely correlated, but the voting privilege threshold is a good way to maintain culture values to some degree.
Correct me if I'm wrong, but given the fact this community was conceived as "an experiment"¹ to explore and empower the hacker community, I suspect one of the points has always been that the "best" ideas float to the top. In this case, the "best" ideas are always relative to the values of the community as a whole; the sum of criteria of the engaged participants, a very diverse audience.
That diverse audience can have multiple motives to vote up or down, according to each individual mindset; it can be agree/disagree, constructive/non-constructive, as you proposed, yes, but it also can be interesting/uninteresting, like/dislike, kind/unkind. Or many other criteria that are not necessarily antonyms; amazing/disgusting, enlightening/TLDR, etc.
So this singular up/down "un-opinionated" system's simplicity allows a cognition diversity one-size-fits-all dynamic, any change in UX would have to be planned for a justifiable purpose and very carefully executed.
It's a bit like when you have a survey and you have 5 or 6 options ranging from 'hate it' and 'love it'.
The difference is often very small and just adds not really necessary options which makes making a choice harder.
How about checking if a user downvoted more than e.g. average number of comments on some post, resulting in his downvotes carrying very little weight if it is true. Unless it's being done already.
