Don’t forget Discus’s PCification (discontinuance) of the down-voting system a few years back. “Up” votes are publicly tallied, “Down” votes are not. Only Up votes (participation trophies) are visible. You can down vote a comment, but no numbers show up. Can’t hurt anyone’s feelings.
Yes, Disqus blocked "negative" votes few years ago. I am convinced it was because liberal comments were massacred with downvotes, while conservative ideas were triumphed. So they rigged the system.