2. FB promotes content with the fastest growth of attention: upvotes, downvotes, comments. It's the opposite of HN, basically. The most engaging content doesnt have to be divisive, but since the majority are emotional beings, and have little interest in abstract thoughts, they react better to emotions. Maybe in a few centuries, the majority will be more concerned with thoughts, and less with emotions, and the equivalent of a flame war will be snarky scientists exchanging with obscure arguments about correctness of some irrelevant theorem, e.g. NP-deniers would reject the NP=P equality, NP-protagonists would support it, and the moderate minority would advocate for a middle ground - that neither statement is provable. Those moderates will be dismissed as Goedel-ists.

3. FB is like a big open club that admits anyone and everyone, and all events take place in the only hall room. Predictably, it turns into a shouting match and FB has to ban some members, and by banning some and not others ideas, the club necesserarily turns into an echo chamber.