Re: Security from whom?
"However, nothing stops Facebook technically from sending a copy of the cleartext prior to encryption to a third party."
Exactly as is the case now. The difference is that the message will be hidden from the large number people and organizations who previously could view it while in transit, only one of them being the NSA. And someone who has your public key is not better off in being able to read the message than someone who does not.
Biting the hand that feeds IT
