2. If this were true, why would we need the Bill of Rights? The entire point of the Fourth Amendment, for example, is to protect citizens against unreasonable searches -- by law enforcement.
3. This would be true if the data were only shared on a need to know basis, which has not been demonstrated. Facebook allows users to give it data under one set of pretenses, and then turns around and uses/sells this data under a different set. I agree the other questions are important, but none of them would be possible if Facebook were not abusing its role.
The NSA FISA orders are getting endless complaints, and yet Verizon and others are handing this data over under a "court" order. In this case, Facebook is doing effectively the same thing, but for profit.