I also don't get why everyone feels FB owes them a dislike button. It seems like that would be a bad feature.
Personally, I think it's a good change. It won't change Facebook much, but it certainly won't do harm.
On the aggregate, however, I see it as a horrendously difficult feature to design adequately.
Simply, for around a month we've been challenged to consider, is a dislike button something you might use? "Ok I suppose YES". Well then here's the new features. "Wait?! Where the dislike button you mentioned?". "Dislike! And crap that reminds me you didn't add the dislike button I want to use right now to dislike that you left the button out!!"
"It's important to give people more options than just 'like'" to help express empathy and sympathy, Zuckerberg said. "Not every moment is a good moment."
"Some people have asked for a dislike button because they want to say, 'That thing isn't good.' And that’s not something that we think is good for the world. So we’re not going to build that," Zuckerberg said at the time.
http://www.usatoday.com/story/tech/2015/09/15/facebook-worki...
I don't like the idea of a dislike button myself but was commenting that unfulfilled expectation was the thing that lead the peanut brigade to whining.