We'll have to agree to disagree. I can't square the logic that it's unconstitutional for the NSA to do this and legal for Facebook and yet somehow it makes sense to argue that it's ok for the NSA but not Facebook.
The government can kill me; Facebook cannot. The government can imprison me; Facebook cannot. The government can require I pay taxes; Facebook can not.
It shouldn't be surprising when similar disparities exist on surveillance. The NSA's program has yet to be deemed unconstitutional by the courts, which is what matters.