The decision by Colin Kaepernick, a quarterback for the San Francisco 49ers, first to sit and then to kneel, rather than stand, during the national anthem before his team’s games has set off a national debate. The 49ers grudgingly supported his right to protest against the ritual, and other players have now joined him, while some politicians, like Senator Ted Cruz, of Texas, have denounced the defiant, if silent, gestures. The best answer to the anthem conundrum, however, can be found in the most eloquent opinion in the history of the Supreme Court.

Kaepernick refused to stand as a form of political expression—to protest, he said, the oppression of African-Americans by the police and others. The Supreme Court case arose out of a related First Amendment right—to exercise the freedom of religion. In 1943, at the height of the Second World War, the court heard a challenge by a Jehovah’s Witness family to the expulsion of their daughters, Marie and Gathie Barnette, from a school in West Virginia. The sisters had been punished for refusing to salute the flag and repeat the Pledge of Allegiance, something state law required of students. (As Jehovah’s Witnesses, the parents did not believe in making such salutes and oaths.) Precedent was not on the Barnettes’ side. In 1940, the Court had heard a very similar case involving Lillian Gobitis, age twelve, and her brother William, age ten, whose parents were also Jehovah’s Witnesses and who were expelled from the public schools of the town of Minersville, Pennsylvania, for refusing to salute the national flag. In an eight-to-one decision in Minersville v. Board of Education, written by Felix Frankfurter, the court rejected students’ claim that their freedom of religion and speech should void the school’s decision to expel them. (Justice Harlan Stone was the lone dissenter.) “National unity is the basis of national security,” Frankfurter wrote. “Conscientious scruples have not, in the course of the long struggle for religious toleration, relieved the individual from obedience to a general law not aimed at the promotion or restriction of religious beliefs.”

What followed, three years later, was one of the great reversals in Supreme Court history. The Court had a new member—Robert Jackson.* More important, even amid the patriotic displays associated with the mobilization for war, the degradations of Nazi Germany had impressed themselves upon the American conscience. The result of the case flipped the result to a six-to-three victory for the family, and Jackson’s opinion in West Virginia State Board of Education v. Barnette stands as perhaps the greatest defense of freedom of expression ever formulated by a Supreme Court Justice—and, not incidentally, a useful message for the N.F.L.

The core idea in Jackson’s opinion is that freedom demands that those in power allow others to think for themselves. In nearly every line, Jackson’s opinion is haunted by the struggle on the battlefield against, in his phrase, “our present totalitarian enemies.” “Struggles to coerce uniformity of sentiment in support of some end thought essential to their time and country have been waged by many good, as well as by evil, men,” Jackson wrote. “Those who begin coercive elimination of dissent soon find themselves exterminating dissenters. Compulsory unification of opinion achieves only the unanimity of the graveyard. It seems trite but necessary to say that the First Amendment to our Constitution was designed to avoid these ends by avoiding these beginnings.” Such melodramatic phrasing may feel more appropriate for the worldwide crisis of that era than for the present one, but the message of tolerance also resonates on the less fraught setting of a football gridiron.

Another central idea in Jackson’s Barnette opinion is that the authorities must trust citizens to make their own choices about whom and what to believe. As he put it,

To believe that patriotism will not flourish if patriotic ceremonies are voluntary and spontaneous, instead of a compulsory routine, is to make an unflattering estimate of the appeal of our institutions to free minds. We can have intellectual individualism and the rich cultural diversities that we owe to exceptional minds only at the price of occasional eccentricity and abnormal attitudes. When they are so harmless to others or to the State as those we deal with here, the price is not too great. But 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.

The phrase “compulsory routine” aptly describes the current tradition of athletes standing for the national anthem. As Jackson reminds us, the ritual will actually mean more—it will reflect the players’ affirmative belief in the United States—if athletes have the choice of whether to stand or not.

The peroration that closes the opinion in Barnette speaks only of the power of government, but the same idea applies to the N.F.L. Americans cannot—and should not—be told what to think or say or express. “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, or force citizens to confess by word or act their faith therein. If there are any circumstances which permit an exception, they do not now occur to us.” To which one might add (switching sports): play ball.

*This sentence has been changed to clarify which justices had recently joined the Supreme Court.