Michael Moore discussed TV news in Bowling for Columbine: scary news glues eyeballs to TV sets, and glued eyeballs are better for ads. So probably by accident Facebook ended up with the same system. Not just scary, I'd wager emotional stuff drives up engagement (imagine a political argument of people screaming "YOU'RE WRONG!") , and Mark and Jack could probably hear the kaching of those ad views.

Also how screwed up is the media landscape in the USA. Political news, and then ads for political candidates. In 2008 the media kept blaring about the "tight race" between Obama and Clinton, and then later on between Obama and McCain. Hmm, were they being honest or did they want to keep eyeballs glued to sell ads? Also political ads?