Content Moderation
And by machine-learning, Facebook may well mean a small army of poorly paid human content-moderators.
The PBS series Independent Lens recently aired a documentary film on these content moderators called "The Cleaners." Available to watch online here: https://www.pbs.org/independentlens/films/the-cleaners/. I highly recommend it.
On a related note, Frontline (another PBS program) recently did a two-part series on Face Book called "The Face Book Dilemma". It's an excellent primer to share with your friends who don't understand what all the fuss is about. Also available to watch online, here: https://www.pbs.org/wgbh/frontline/film/facebook-dilemma/
Biting the hand that feeds IT
