In a stinging dissent to a 1961 Supreme Court decision that allowed the Illinois state bar to deny admission to prospective lawyers if they refused to answer political questions, Justice Hugo Black closed with the memorable line, "We must not be afraid to be free." Black saw the First Amendment as the foundation of American freedom--the guarantor of all other Constitutional rights. Yet since free speech is by nature unruly, people fear it. The impulse to curb or limit it has been a constant danger throughout American history.

In We Must Not Be Afraid to Be Free, Ron Collins and...