Freedom to differ is not limited to things that do not matter much. That would be a mere shadow of freedom. The test of its substance is the right to differ as to things that touch the heart of the existing order. If there is any fixed star in our constitutional constellation it is that no official, high or petty, can prescribe what shall be orthodox in politics, nationalism, religion or other matters of opinion.
-- Supreme Court Justice Robert H. Jackson, writing for the majority in West Virginia Board of Education v. Barnette (319 U.S. 624), ruling that public school children could not be compelled to salute the U.S. flag (1943)