In a 5-4 decision yesterday, the U.S. Supreme Court declared unconstitutional Washington, D.C.’s, ban on possession of handguns in people’s homes. Rejecting the ridiculous argument of the gun controllers that the Second Amendment is intended to protect the “right” of the National Guard to own guns, the Court correctly held that our American ancestors intended to protect the right of private individuals to keep and bear arms.

The decision is especially important for people in D.C., which is oftentimes labeled “the murder capital of the nation.” Many of the murders in D.C. are committed with handguns. How is that possible, given that it’s illegal to own handguns in D.C.? Because murderers have steadfastly refused to obey D.C.’s gun ban, which means that the law has prevented victims from defending themselves from murderers with handguns.

But there’s another reason for the Second Amendment, one that even the most stalwart gun-rights advocates are oftentimes reluctant to mention in polite conversation. The real reason that the Framers specifically enumerated people’s right to keep and bear arms was to enable the citizenry to defend themselves from tyranny at the hands of U.S. government officials.

After all, let’s not forget that the people who crafted the Second Amendment had been British citizens who took up arms against their own government. If they had not been free to own guns, those English colonists would never have been able to revolt against the tyranny of their own government. When the English troops came to kill them (and confiscate their guns), the colonists were able to successfully defend themselves — because they had guns that they could use to shoot back.

Of course, gun-control advocates say that tyranny happens only in foreign countries, such as Britain, and that it could never happen here in the United States. Never mind that U.S. officials are now kidnapping, torturing, sexually abusing, murdering, and incarcerating people in secret prisons and denying people due process, trial by jury, and protection from cruel and unusual punishments, but, heck, those are foreigners, not Americans, right? Well, except for American citizen Jose Padilla but, heck, he’s only one American. No cause for concern there, right? And the president and Congress have cancelled habeas corpus only for foreigners. They would never do it against American citizens, right?

Well, the truth is that one never knows. I’m willing to bet that when the members of the German parliament granted their president’s request to “temporarily” suspend civil liberties during the German terrorist and communist crisis, most Germans never figured that their government would become tyrannical. But as they learned, once the darkness of tyranny falls upon a nation it’s a bit too late to start calling for gun rights.

The right to keep and bear arms is the ultimate insurance policy against tyranny. Like most other insurance policies, the probability is that a claim will never be made upon it. But if disaster were to strike, people who love liberty will be happy that they preserved the right — and the ability — to resist. Moreover, the existence of such a policy is the best way to ensure that federal officials think twice before going too far with their tyrannical dreams.

Mr. Hornberger is founder and president of The Future of Freedom Foundation.