Every idea is an incitement. It offers itself for belief and if believed it is acted on unless some other belief outweighs it or some failure of energy stifles the movement at its birth. The only difference between the expression of an opinion and an incitement in the narrower sense is the speaker’s enthusiasm for the result.

Justice Holmes dissenting, Gitlow v. New York, 268 U.S. 652, 673 (1925).