Hacker News has a similar problem with comments: net_votes = up_votes - down_votes You need at least two of the above variables to get an idea of both the direction and magnitude of the voting. Hacker News provides only one: net_votes. YouTube used to provide up_votes and down_votes, effectively providing all three. Now YouTube has reduced its information to up_votes, so they're now down to one variable in the equati…
Because on HN there are only two possible states for comments. Flagged or visible. The upvotes and downvotes just help compute the order. This is better for freedom of expression and showing the split would be a bad idea imo. Comments who are more upvoted are also more downvoted because they are more visible (as they rank first)
That's an oversimplification; downvotes may also reduce the visibility of comments by making them an eyebleeding gray-on-white.