I've been making my way through this presentation by Maciej Cegłowski
Some kinds of services are just crying out for decentralization. Fifty years from now, people will be shocked that we had one social network that all seven billion people on the planet were expected to join.
Imagine if there was only one bar in Düsseldorf, or all of Germany, and if you wanted to hang out with your friends, you had to go there. And when you did, there were cameras everywhere, and microphones, and you were constantly being interrupted by people selling you stuff. That's the situation that obtains with Facebook today.
Surveillance as a business model is the only thing that makes a site like Facebook possible.