Having opposites (Like/Dislike, Up/Down) is natural and Facebook tried to create behaviour which is not natural. I think this is a great proof that Businesses have to adapt to the users and not the other way around.
Few people post a news article to facebook because they want a healthy debate on it, they do it because they want to get general agreement from their friends and family. The people who go on and start arguments in the comments are pretty universally hated in my experience. Nobody likes scrolling through the news feed and seeing drama drama drama.