Hmm. For me the dislike button was informative. If feels like they are trying to create a world where everything can only be good, better, even more better, which just doesn't represent reality. Imagine Stack Overflow only having the option to upvote Questions and Answers. The ratio of likes vs dislikes of a TED talk does help me to decide if I should stop watching a video which just isn't getting better.
Hiding dislikes is something Brands want.