The key value of Facebook is mass-opt-in messaging, including photos/videos as a sort of message. So if I'm going to such and such a party, I don't need to seek

The key value of Facebook is mass-opt-in messaging, including photos/videos as a sort of message. So if I'm going to such and such a party, I don't need to seek people out, I just post it on Facebook and people will know what I'm up to if they want to join. Until a service exists and I can migrate there with all of my friends, I need Facebook to fill that role. Yeah, I could just restrict myself to those who seek me out (or I seek out), but that would likely mean discarding some people who might have been great lifelong friends.