From Stewart's concurrence:
[...]
Yet it 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. I should suppose that moral, political, and practical considerations would dictate that a very first principle of that wisdom would be an insistence upon avoiding secrecy for its own sake. For when everything is classified, then nothing is classified, and the system becomes one to be disregarded by the cynical or the careless, and to be manipulated by those intent on self-protection or self-promotion. I should suppose, in short, that the hallmark of a truly effective internal security system would be the maximum possible disclosure, recognizing that secrecy can best be preserved only when credibility is truly maintained. But, be that as it may, it is clear to me that it is the constitutional duty of the Executive -- as a matter of sovereign prerogative, and not as a matter of law as the courts know law -- through the promulgation and enforcement of executive regulations, to protect the confidentiality necessary to carry out its responsibilities in the fields of international relations and national defense.
This is not to say that Congress and the courts have no role to play. Undoubtedly, Congress has the power to enact specific and appropriate criminal laws to protect government property and preserve government secrets. Congress has passed such laws, and several of them are of very colorable relevance to the apparent circumstances of these cases. And if a criminal prosecution is instituted, it will be the responsibility of the courts to decide the applicability of the criminal law under which the charge is brought. Moreover, if Congress should pass a specific law authorizing civil proceedings in this field, the courts would likewise have the duty to decide the constitutionality of such a law, as well as its applicability to the facts proved.