The United States managed to remain neutral during the first few years of World War I.

In 1915, after an uproar over the sinking of the ocean liner Lusitania – which resulted in the death of 128 U.S. citizens – Germany ordered its submarines not to attack neutral shipping. That reprieve lasted until February 1917, when Germany “resumed unrestricted submarine warfare against all ships in the war zone.”

That development – coupled with the discovery of a telegram from the German foreign minister to the country’s ambassador in Mexico “offering United States territory to Mexico in return for joining the German cause” – prompted the U.S. to finally join the war in April 1917. (For those interested in the history of this period, Barbara Tuchman wrote a fascinating book on the Zimmerman telegram.)

Two months after the U.S. declared war, Congress enacted the Espionage Act of 1917, which prohibited collecting information on national defense meant to harm the United States (i.e. spying) and “created criminal penalties for anyone obstructing enlistment in the armed forces or causing insubordination or disloyalty in military or naval forces.”

This latter element of the bill led to a number of important, precedent-setting legal cases. In Schenck v. United States, Justice Oliver Wendell Holmes Jr. wrote the majority opinion, which upheld the conviction of two activists for sending a letter to conscripted soldiers that compared the draft to involuntary servitude. The opinion included the famous hypothetical of a person shouting fire in a crowded theater. The decision established the principle that during wartime, the government might be able to restrict speech in ways it might not under other circumstances – if the speech represented a clear and present danger.

Interestingly, though, Holmes dissented in a similar case, Abrams v. United States. That case involved Russian immigrants who distributed literature opposing U.S. intervention in the Russian civil war. In this instance, Holmes felt the actions did not pose any real danger to the nation. His dissenting opinion advanced a well-known justification for stringent protection of free speech:

when men have realized that time has upset many fighting faiths, they may come to believe even more than they believe the very foundations of their own conduct that the ultimate good desired is better reached by free trade in ideas – that the best test of truth is the power of the thought to get itself accepted in the competition of the market, and that truth is the only ground upon which their wishes safely can be carried out. That, at any rate, is the theory of our Constitution. It is an experiment, as all life is an experiment. Every year, if not every day, we have to wager our salvation upon some prophecy based upon imperfect knowledge. While that experiment is part of our system, I think that we should be eternally vigilant against attempts to check the expression of opinions that we loathe and believe to be fraught with death, unless they so imminently threaten immediate interference with the lawful and pressing purposes of the law that an immediate check is required to save the country.

Consistent with this principle, the current approach to free speech is to allow almost entirely unfettered speech, even when that includes allowing truly vile speech and actions (that don’t directly harm another person).

Putting aside whether listening to every possible opinion is actually the best way to discern truth (exposure to Nazi propaganda is not likely to lead to greater understanding, for instance), there are lessons from the Supreme Court’s extremely broad protection of speech for parallel matters like religious freedom.

First, we don’t have to accept the truth claims of another person’s speech to find it worthy of protection. Similarly, we don’t have to share the beliefs of another religion, or of a non-religious person, to recognize the value in protecting their right to practice those beliefs.

Second, the free speech cases teach us an appropriate skepticism about the government’s ability to pick between messages that should be promoted and those that should be proscribed. Common sense tells us that when state power is used to squelch the practices of others – even (or especially) those with whom we fundamentally disagree – we may, at some point in the future, be subject to the same treatment. Carefully making room for beliefs and practices we find objectively wrong may still have the effect of widening our own circle of freedom.

There are limits to both free speech and free exercise of religion. The Constitution does not shield obscenity or slander. It does not protect the right of a religious group to commit acts such as taking another’s life as part of their ceremonies, no matter how sincere.

Even with these limitations, there is plenty of room for a wide diversity of manifestations of belief in speech and religious practice. This is probably necessary in our pluralistic society: not so much to help us decide between alternatives, but to be assured that when we need to act on our beliefs or share our fundamental ideas, we will have space to do so free from government interference.