All speech should be presumed to be protected by the Constitution, and a heavy burden should be placed on those who would censor to demonstrate with relative certainty that the speech at issue, if not censored, would lead to irremediable and immediate serious harm.
Dershowitz, Alan (2008). Finding, Framing, and Hanging Jefferson: A Lost Letter, a Remarkable Discovery, and Freedom of Speech in an Age of Terrorism. John Wiley & Sons. p. 30. ISBN0470450436.