The problem is that you can't aggregate them. 1 Like and 4 dislikes = "20% like this". What are you going to do with a bunch of faces to show consensus? And which of those faces am I supposed to use to say this post is filled with misinformation and you shouldn't be spreading it ... Angry? Sad?
This. They should have worked harder to get useful customer information, that would also benefit the reader. Easily done using multiple scales: Like <-->Dislike Spam <--> More of this, and so on.