In the absence of the governmental checks and balances present in other areas of our national life, the only effective restraint upon executive policy and power in the areas of national defense and international affairs may lie in an enlightened citizenry – in an informed and critical public opinion which alone can here protect the values of democratic government. For this reason, it is perhaps here that a press that is alert, aware, and free most vitally serves the basic purpose of the First Amendment. For, without an informed and free press, there cannot be an enlightened people.
Potter Stewart, Justice of the United States Supreme Court, in his concurring opinion in New York Times v. United States, where the government asked the court to issue prior restraint against the New York Times to prevent it from publishing the Pentagon Papers. The court ruled 6-3 in favor of the Times.
The rest of the opinion, only a few other paragraphs, is worth the read.