In Facebook, we don't have many discussions.
Coming to the subject of Youtube, it is a pay channel. The person who posted the video may get some money based on the likes, watches and comments. That is why in that they have given the option of dislikes. But on
Facebook, no financial benefits are there. I think that is why they have not provided this option on Facebook.
Non-violence is the greatest Dharma; So too is all righteous violence.
Getting dislikes or a thumbs down is not a very likable option anyway.