Our government is the potent, the omnipresent teacher. For good or for ill it teaches the whole people by 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 retributions.