Earlier quoted context omitted.
It seems like it would be a disaster to break up Facebook. You can't really have more than one social network that everybody uses. Forcing everyone to split off into groups wouldn't work, to put it mildly.
But we could have an open social network that operates outside a single company... building on the foundational principles of the internet. These "social networks" exist because it's still too hard to setup and manage a personal website, and those sites lack the interactiveness of FB. Imagine if everyone had their own 1-click website with glorified RSS feeds, webrtc-based chat, access control, media sharing, and stan…
Using email, the rule is that if someone sends you something, you own it; they could ask you to do delete it, but you can refuse. Facebook and other social networks let you edit and delete posts. Snapchat became big because you can send pictures that are automatically deleted after you view them.
Sure, you can reimplement basic message exchange in a decentralized way, but figuring out how to enforce the same rules in a decentralized system is nontrivial.