Once the government can demand of a publisher the names of the purchasers of his publications, the free press as we know it disappears. Then the spectre of a government agent will look over the shoulder of everyone who reads. The purchase of a book or pamphlet today may result in a subpoena tomorrow. Fear of criticism goes with every person into the bookstall. The subtle, imponderable pressures of the orthodox lay hold. Some will fear to read what is unpopular, what the powers-that-be dislike. When the light of publicity may reach any student, any teacher, inquiry will be discouraged. The books and pamphlets that are critical of the administration, that preach an unpopular policy in domestic or foreign affairs, that are in disrepute in the orthodox school of thought will be suspect and subject to investigation. The press and its readers will pay a heavy price in harassment. But that will be minor in comparison with the menace of the shadow which government will cast over literature that does not follow the dominant party line. If the lady from Toledo can be required to disclose what she read yesterday and what she will read tomorrow, fear will take the place of freedom in the libraries, book stores and homes of the land. Through the harassment of hearings, investigations, reports and subpoenas government will hold a club over speech and over the press.[United States v. Rumely, 345 U.S. 41 (1953)]
William O. Douglas