"We are in danger of forgetting that the Bill of Rights reflects experience with police excesses. It is not only under Nazi rule that police excesses are inimical to freedom. It is easy to make light of insistence on scrupulous regard for the safeguards of civil liberties when invoked on behalf of the unworthy. It is too easy. History bears testimony that by such disregard are the rights of liberty extinguished, heedlessly at first, then stealthily, and brazenly in the end." Justice Felix Frankfurter