@elsbet The program is and must be subject to debate, weighing of tradeoffs, and oversight. The problem with subjecting the program to traditional models of those things is that most of the information we'd need to have in order to do those things is not and cannot be available to the general public. Presidents are privy to information that the general public isn't and can't be. We cannot have a national or even a Congressional debate about a largely-secret program that responds to largely-secret needs for the same reason that you can't have a debate about the implications of the Higgs Boson for supersymmetry with a fourth grader. A debate presupposes knowledge of the relevant issues. An opinion, a bare, conclusory assertion, made free of such knowledge, is not a debate position. And without these things, we are weighing two unknown quantities against one another on an invisible scale.
Accordingly, because much of the information that explains why the program is necessary and what the program does is classified, which naturally (although unhappily) places the primary locus of the debate within the executive branch, subject to the judgment of the President, who is charged, before God and history, with protecting this country in light of knowledge that he has but which we may not have. That is a necessary consequence that follows ineluctably from the epistemological limits just described.
That is an extraordinary situation—it's dangerous, and it's constitutionally unusual if not abberant. To be sure, the founding generation were not the neurotic libertarians of today; they understood full well that state secrets came with the executive power that was reposed in the presidency. "Decision, activity, secrecy, and dispatch" must characterize the Presidency, wrote Hamilton in Federalist 70; a legislature "is unfit to exercise the executive power," wrote John Adams in Thoughts on Government, "for want of two essential properties, secrecy and dispatch." Nevertheless, the incipient danger in this situation demands the oversight that is possible while remaining confidential which is where the intelligence committees and the FISA courts come in.
Nevertheless, the primary check on all this is the President himself. And the extraordinary reality thus implied should induce us to be exceedingly careful of whom we elect to the Presidency. This is a balancing act that we need to confide to the President, and because that is an awesome and extraordinary trust, we need to ensure that we are electing serious, sober, experienced, God-fearing men and women whom we can trust. Some of us think that we picked the wrong guy, but so what?
For sake of being clear, I should say explicitly: I am not on the "pro-PRISM" side of the debate between people who are "pro-PRISM" and those who are "anti-PRISM." My claim is that the general public lacks (and cannot be given) the information neccessary to have that debate. That debate, the debate that the "anti-PRISM" folks are keen to have, the weighing of PRISM's utility against its costs, must take place—but I am not taking a side. I am arguing that that debate must and can only take place within the walls of the executive branch. I do not advocate PRISM. I say that we are incompetent to have a valid opinion on it, to advocate for or against it.
Justice Stewart's concurrence in the Pentagon Papers case, and I'll end with this, remains trenchant:
"[I]t is elementary that the successful conduct of international diplomacy and the maintenance of an effective national defense require both confidentiality and secrecy. Other nations can hardly deal with this Nation in an atmosphere of mutual trust unless they can be assured that their confidences will be kept. And, within our own executive departments, the development of considered and intelligent international policies would be impossible if those charged with their formulation could not communicate with each other freely, frankly, and in confidence. In the area of basic national defense, the frequent need for absolute secrecy is, of course, self-evident.
"I think there can be but one answer to this dilemma, if dilemma it be. The responsibility must be where the power is. If the Constitution gives the Executive a large degree of unshared power in the conduct of foreign affairs and the maintenance of our national defense, then, under the Constitution, the Executive must have the largely unshared duty to determine and preserve the degree of internal security necessary to exercise that power successfully. It is an awesome responsibility, requiring judgment and wisdom of a high order."