This is obviously just another similar data point on this thread, but what I want to add is to the discussion is this idea: why not create an completely OSS facebook? If a bitcoin can exist (and hell, a Linux), why not a decentralized open-source facebook? The core functionality is not that complex, IMHO. Well, Linux is complex and it took decades to perfect... but the need for it was pretty clear and it's proved itself. But Facebook, OTOH, is not a complex operating system or even a super-complex search engine (ala Google). It's simply a network of interconnected user accounts with certain assets assigned to each account (history, preferences, content, etc), and info feeds (transient) delivered to those accounts via various formats.
If such a project were OSS, people would design their own feed sorting algo's, their own notification systems, and most of all their own "spam" filtering systems, as plugins, all of which could mean nobody needs to "go dark" to satisfy the whims of one corporate entity.