Together with the other First Amendment guarantees–of free speech, a free press, and the rights to assemble and petition–the Religion Clauses were designed to safeguard the freedom of conscience and belief that those immigrants had sought. They embody an idea that was once considered radical: Free people are entitled to free and diverse thoughts, which government ought neither to constrain nor to direct.
~Justice Sandra Day O’Connor, concurring in McCreary County v. ACLU of Kentucky, 545 U.S. 844 (2005)
The greater the importance of safeguarding the community from incitements to the overthrow of our institutions by force and violence, the more imperative is the need to preserve inviolate the constitutional rights of free speech, free press and free assembly in order to maintain the opportunity for free political discussion, to the end that government may be responsive to the will of the people and that changes, if desired, may be obtained by peaceful means. Therein lies the security of the Republic, the very foundation of constitutional government.
~Chief Justice Charles Evans Hughes, De Jonge v. Oregon, 299 U.S. 353 (1937)
It must never be forgotten, however, that the Bill of Rights was the child of the Enlightenment. Back of the guarantee of free speech lay faith in the power of an appeal to reason by all the peaceful means for gaining access to the mind. It was in order to avert force and explosions due to restrictions upon rational modes of communication that the guarantee of free speech was given a generous scope. But utterance in a context of violence can lose its significance as an appeal to reason and become part of an instrument of force. Such utterance was not meant to be sheltered by the Constitution.
~Justice Felix Frankfurter, Milk Wagon Drivers Union of Chicago, Local 753 v. Meadowmoor Dairies, Inc., 312 U.S. 287, 293 (1941)