FWIW, this is coming very soon to FB in the form of "reactions" rather than a simple "dislike" feature.
http://www.engadget.com/2016/01/27/facebook-reactions-launch...
I'm concerned that all reactions might be treated as good reactions. That is, that there is no way to politely disapprove. Does anyone have any more details on this?
I suspect facebook and company will come up with a solution to the problem of how do you indicate that you saw something without commenting when it's not socially acceptable to 'like' it. For example a funeral announcement, you don't want to 'like' it but you want to say 'thank you' or something yet you might not want to comment.
A real dislike or hate button would simply result in a lower signal/noise ratio. Maybe new types of bullying where lot's of people 'hate' on somebody.