Oliver Wendell Holmes, Jr. Quote

The most stringent protection of free speech would not protect a man in falsely shouting fire in a theater and causing a panic.... The question in every case is whether the words used are used in such circumstances and are of such a nature as to create a clear and present danger that they will bring about the substantive evils that Congress has a right to prevent.

Schenck v. United States, 249 U.S. 47 (1919)