"The predominant purpose of the grant of immunity here invoked was to preserve an untrammeled press as a vital source of public information. The newspapers, magazines and other journals of the country, it is safe to say, have shed and continue to shed, more light on the public and business affairs of the nation than any other instrumentality of publicity, and, since informed public opinion is the most potent of all restraints upon misgovernment, the suppression or abridgement of the publicity afforded by a free press cannot be regarded otherwise than with grave concern. The tax here involved is bad not because it takes money from the pockets of the appellees. If that were all, a wholly different question would be presented. It is bad because, in the light of its history and of its present setting, it is seen to be a deliberate and calculated device in the guise of a tax to limit the circulation of information to which the public is entitled in virtue of the constitutional guaranties. A free press stands as one of the great interpreters between the government and the people. To allow it to be fettered is to fetter ourselves."