As long as HN has a number assigned to everyone that people interpret as significant, I'm completely for downvoting without any explanations. The fact that both upvoting and downvoting are anonymous (to the one getting the votes) ties directly with this, IMO.
One of: off-topic, incorrect, me-too, troll, spam.
I bet though a lot of people would still use incorrect for disagreements.
I always thought slashdot had a great moderation system where +5 was the max a post could get and everyone only had a few votes every few weeks so you had to be careful. The upvotes also had reasons like (insightful, funny, interesting ..) so a user could sort by those.
One of: off-topic, incorrect, me-too, troll, spam
I suggested such a metric for flags to dang over a year ago, and I wouldn't assume that I was the first to do so.Drive by downvoting is often by people who aren't willing to pause and share their why.
It might not be easy to reflect on whether one is as open minded or comfortable to look at their own views, or openly entertain a viewpoint that isn't their own.
Innovative and disruptive thought may not exist in agreeable form even for a place as forward thinking as HN may imagine itself to be.