I agree with you, but the claim that Facebook is decrypting and reencrypting things is a very very very severe one.

I didn't claim they are. But they can. And without transparency, I have very little inclination to trust. I find it plausible that they'd scan for keywords and phone home when they get hits -- advertising businesses are not known for their scruples and fb has not distinguished itself in that regard. Once that machinery is in place, it's ripe for abuse. I don't claim any proof it's happening, but it would be naive to blindly trust that it isn't.