"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." - Justice Bandeis Dissent in Olmstead, 1928

link to the full dissent