A recent post by former BBC North American editor Justin Webb expresses puzzlement at the pattern of gun ownership in the U.S., reporting that the zip code he used to live in, an area safe enough so that people routinely left their doors unlocked, had a surge of gun purchases after the Supreme Court found unconstitutional the D.C. ban on handgun ownership. He thinks it is obvious that his one-time neighbors have no need for guns to protect themselves, and attributes the pattern to a peculiarly American belief in a link between private ownership of firearms and political freedom.I have no idea whether his facts or his interpretation are correct; his post does not provide any link to his data source on handgun purchases, leaving open a variety of other explanations. He is surely correct, however, that many Americans see private ownership of firearms as something that makes tyranny less likely.The interesting question is why. Webb takes it for granted that the underlying argument is that firearms make rebellion against oppression easier, and that is indeed an argument common among supporters of the Second Amendment. He points out, as evidence against, that we have just had an example of a successful rebellion in Egypt, and private firearms played no significant role.As it happens, I agree with the view that private ownership of firearms helps prevent tyranny. But I don't think the main reason is that it makes rebellion easier. That argument was plausible in the 18th century, and probably played a considerable role in the writing of the Second Amendment. But changes since then make it a much weaker argument now. The gap between private weaponry and military weaponry has become much larger, as has the size of the professional military. Part of the original theory, at least as I read it, was that a large militia made a large professional army unnecessary.In my view, the real argument for private firearm ownership is a different one. The less able individuals are to protect themselves from crime, the more dependent they are on protection by government law enforcement. The more dependent they are on protection by government law enforcement, the more willing they will be to accept abuses by government law enforcement. The more willing we are to be pushed around by the police, the harder it will be to prevent a tyrannical government from arising. Indeed, in some contexts, most obviously the War on Drugs, one can argue that one has already arisen. And been tolerated.