>It's promoting behavior that is different from real life as they stand to gain from stoking outrages and heated discussions: more active user engagement!
This undoubtedly has very serious consequences beyond merely being annoying.
Trending untrue news stories, encouraging post-true controversy and providing an echo chamber for these things to intensify and become ingrained.
And doing these things on a enormous scale to a huge percentage of the population such that vast swathes of people can no longer even agree on basic facts.
It would be interesting to see how much of the bizarre political events in the west are a result of social media in general and Facebook in particular.