Totally agreed. The law should reflect our morals. But we judge the legality of an action by the law, not our morals.
Moreover, the problem for privacy advocates is that the moral debate is even less clear than the legal one. Being able to declare the NSA's actions straight-up unconstitutional under the 4th amendment would avoid the mess of resorting to the democratic process to determine what the people, as a whole, really thought about surveillance.
The law should be a reflection of our morals, not the other way around. That would be a recipe for disaster.