Quote from Justice William O. Douglas,
"Once the government can demand of a publisher the names of the purchasers of his publication, the free press as we know it disappears. Then the spectre of a government agent will look over the shoulder of everyone who reads. ... 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. ... fear will take the place of freedom in the libraries, book stores, and homes in the land."