Ask HN: Why does HN allow downvoting without explanation?

Because the last thing HN needs is more bickering about downvotes, and such 'explanations' would bring a deluge of it.

Because downvote already says that the comment did not add anything of value to that specific discussion in context. Now you might say that what if someone disagrees with a comment and incorrectly downvotes ? In that case, an explanation will not be useful anyway because the person has already downvoted.

The purpose of downvote is to get rid of comments that are of no value and in my experience being on HN for a few years, it works pretty well for majority of the time. Yes, I am sure people downvote incorrectly but this is the internet. You cannot expect everyone to be on their best behavior. But again, most of the downvotes in HN seem appropriate to me at least.

How would an explanation help? Sladhdot had upvotes with a choice of descriptions (funny/etc.). HN in general is historically against making any improvements to the interface. You could dream of thousands of improvements to HN's UI, but the bar is the sky...