
First as to speech.  That privilege rests upon the premise that
there is no proposition so uniformly acknowledged that it may not be
lawfully challenged, questioned, and debated.  It need not rest upon
the further premise that there are no propositions that are not
open to doubt; it is enough, even if there are, that in the end it is
worse to suppress dissent than to run the risk of heresy.  Hence it
has been again and again unconditionally proclaimed that there are
no limits to the privilege so far as words seek to affect only the hearers'
beliefs and not their conduct.  The trouble is that conduct is almost
always based upon some belief, and that to change the hearer's belief
will generally to some extent change his conduct, and may even evoke
conduct that the law forbids.

[cf. Learned Hand, The Spirit of Liberty, University of Chicago Press, 1952;
The Art and Craft of Judging: The Decisions of Judge Learned Hand,
edited and annotated by Hershel Shanks, The MacMillian Company, 1968.]
