Youtube comments currently look like this:
When you upvote a comment, the "thumbs up" symbol becomes blue for you and one point gets added to the score immediately, making it look like this:
When you downvote a comment, the "thumbs down" symbol also becomes blue for you. However, nothing is subtracted from the comment score. Nor does YouTube display the downvotes separately. Instead, it looks like this:
What does YouTube actually do with the downvotes?
I'm assuming it's something considering they have a downvote button at all. (As opposed to the "up only" approach of SE comments, for example, which would be the logical choice if downvotes didn't do anything anyway.)
Does it have anything to do with which comments get displayed and which don't? Is it some sort of under-the-hood stuff that most users won't understand?