From Olmstead vs US 1928.
The point is thus stated by counsel for the telephone companies, who have filed a brief as amici curiae:
“Criminals will not escape detection and conviction merely because evidence obtained by tapping wires of a public telephone system is inadmissible, if it should be so held; but, in any event, it is better that a few criminals escape than that the privacies of life of all the people be exposed to the agents of the government, who will act at their own discretion, the honest and the dishonest, unauthorized and unrestrained by the courts. Legislation making wiretapping a crime will not suffice if the courts nevertheless hold the evidence to be lawful.”
BTW, Snowden is a patriot to joust with the NSA and its illegal wiretaps.
The following quote from Olmstead v. U.S. 1928 is instructive:
Decency, security, and liberty alike demand that government officials shall be subjected to the same rules of conduct that are commands to the citizen. In a government of laws, existence of the government will be imperiled if it fails to observe the law scrupulously. Our government is the potent, the omnipresent teacher. For good or for ill, it teaches the whole people by its example. Crime is contagious. If the government becomes a lawbreaker, it breeds contempt for law; it invites every man to become a law unto himself; it invites anarchy. To declare that in the administration of the criminal law the end justifies the means-to declare that the government may commit crimes in order to secure the conviction of a private criminal-would bring terrible retribution. Against that pernicious doctrine this court should resolutely set its face.
MR. Justice Brandeis, dissenting.