Have always felt that there is something missing when discussing something serious on Facebook, what do you think ?

Yes, You are absolutely right

Facebook has lost the ability to engage people in serious discussion because there are too many channels of communication. If I like a political post and present my view, it is subjected to the whims of any on looker. Said on looker can come from my network or someone elses. Which leaves room for slander, trolling, and any other type of attention. Sadly, this makes for a poor format.

Facebook is subject to the same social taboos that the rest of the world is subjected to. Imagine you are at a party and the topic of Sandy Hook comes up. Less worrisome than someone hearing you talk about Sandy Hook is the idea that serious discussion on such a massive tragedy is not meant to be discussed at a party. Everything you say must conform to social cues. Like a real party, Facebook is made up of your friends and your acquaintances. It is not a public forum where people you do not know can participate: you are debating serious topics with people you would normally discuss no more than the weather with. Facebook, to most of your acquaintances, proves your wit and success as a person, like an office party.

While I mostly agree with what's been said here, I believe Facebook has one advantage over other sites for discussion: you're likely to get a vast array of opinions. Blogs and publications run the risk of becoming echo chambers. If I blog about liberal things, for instance, I'm likely to attract liberal readers. Even if conservative folks come by every so often, they aren't likely to feel safe in an all-liberal environment. However, FB's strength is precisely its ability to reach every person you know. I may not be thinking about my politically dissident friend when I post something, but he's just as likely to comment on my post as anyone else. In that respect (diversity of opinions), FB might be the best place for discussion.