The youtube dislike button did the exact opposite of what everyone thought it did (at least it DID for a significant length of time).

It promoted the video. Any end user interaction was/is considered positive for any video. Disliking a video was/is no different. Honestly not sure if it did or does much for comments either. And the whole "people will see negative dislikes and see people dislike it for some reason and hopefully learn why" might work somewhat, but is largely cope. People aren't going to look at it 95% of the time.