Why would Facebook, you ask?
It's a legitimate question. Because nobody in their right mind trusts FB with their private communication now, do they? But if FB stands their ground, afterwards everyone *will* trust them. Then, later when the governments mandate backdoors, and they redesign their architecture to be client-server so that the NSA et al can put in hooks to grab that data (see also Skype), nobody will compain and they'll still treat it as secure and private. Everybody wins, except for of course nobody wins.