> We’ve lost half the potential information. If a post has zero upvotes, does that mean it’s bad? incorrect? uninteresting? mediocre? There’s no way to tell, because zero has multiple meanings.

Having downvotes doesn't fix this problem. You still loose information. If a post has zero upvotes, does that mean nobody cares, or a lot of people love it, and the same number hate it? The only site that gets this right is youtube: It shows both likes and dislikes.