I used to challenge people with this on Reddit and the results were sometimes silly ridiculous. In an echo chamber like environment people sometimes downvote because they are compelled by the gravity of Reddit’s visible vote count and sometimes because they are willfully using a downvote as a blunt weapon to suppress a challenging opinion. Yet when you compel people to put that into words the results are clearly a form of cognitive complexity with people twisting themselves into knots to describe their own behavior in a meaningful way. That absurdity aside I would notice that the challenge of asking people to qualify their downvote would slow or halt the pace of the echo chamber foolishness.

HN is not Reddit though. The maximum downvote count is 5 reducing a comment to a score of -4 and aside from the color fading of negativity scored comments vote counts are not published. The majority of users and discussions are also generally superior to those of Reddit as well.

Even with that said problematic discussions do happen on HN even if far more rarely. The reason for the problematic behavior, as many people clearly identify, is people looking for agreement more than discussion or insight. In this case people on HN engaging conversations only for agreement are generally eager to advertise their censoring foolishness and insecurity.

Aside from contrived political discussions downvotes are generally reserved for comments that are far off topic or impose violating behavior.

Either way the biggest change this would result is visibly associating a user to their down vote. Otherwise, I don’t see this having a dramatic impact on HN. This would have a huge impact at Reddit though.