in case you didn't heard http://venturebeat.com/2015/06/01/hands-on-with-facebooks-new-pgp-encryption-features/ So now i guess having a PGP key program at your pc will look less suspicious.
EDIT: Obviously i never said to use the same key to Facebook as at the DNMs. Or to fucking use a key at all.
FB will still have access to the data before they encrypt it, which they could store in plain text before encrypting it.