Foxies
I voted no, even though I can see merit in the idea that you can let people know their post is not appreciated. But it is a bit harsh, not specific enough, and can lead to more arguments.
Being able to add emoticons as a reaction would be more specific, and with the right emoticons can be less confrontational that a unspecified dislike. And it would also allow you to give a more precise positive reaction to the post, so you don't need to add another post, and keep the discussion more compact. (I'm only saying that it would give an extra option, not discourage people from giving short reactions.)