Except, people like to use Facebook as a broadcast medium, and the message size is likely to get prohibitively large if you're encrypting to a lot of people.
Do you have any evidence of this strange claim?
Encrypting a message to lots of recipients in an efficient way has been solved for email (via OpenPGP / GPG) a long time ago.
It is a positive side effect of the hybrid algorithms which combine symmetric with asymmetric algorithms, originally introduced to reduce computation time for classic (single-recipient) asymmetric cryptography.
I guess I was thinking more along the lines of the actual network it sits on will help, too. Like CJDNS, an added protective layer for privacy, at least.
Public key encryption generated automatically for each user using the freedom box (I think I watched a video of someone explaining their concept of this for the freedom box).
In the end, I don't know. I'm only starting to get involved.