The government doesn't have to resort to conspiracies to get your personal data from Facebook, if it wants it, it can get it. We live in the age of PRISM (in which Facebook is a participant,) secret orders, and NSA bulk surveillance. They could literally just build or hack an app that uses Facebook's API, apparently, or buy something from the black market, or in the narrow case get a warrant.

Not to mention... I don't think this would actually give anyone "Legal authority to examine all that juicy personal data Facebook holds." I don't think "legal authority" actually works that way, but IANAL.