Guns are dangerous. But myths are dangerous, too. Myths about guns are very dangerous, because they lead to bad laws. And bad laws kill people. "Don't tell me this bill will not make a difference," said President Clinton, who signed the Brady Bill into law. Sorry. Even the federal government can't say it has made a difference. The Centers for Disease Control did an extensive review of various types of gun control: waiting periods, registration and licensing, and bans on certain firearms. It found that the idea that gun control laws have reduced violent crime is simply a myth. I wanted to know why the laws weren't working, so I asked the experts. "I'm not going in the store to buy no gun," said one maximum-security inmate in New Jersey. "So, I could care less if they had a background check or not." "There's guns everywhere," said another inmate. "If you got money, you can get a gun." Talking to prisoners about guns emphasizes a few key lessons. First, criminals don't obey the law. (That's why we call them "criminals.") Second, no law can repeal the law of supply and demand. If there's money to be made selling something, someone will sell it. A study funded by the Department of Justice confirmed what the prisoners said. Criminals buy their guns illegally and easily. The study found that what felons fear most is not the police or the prison system, but their fellow citizens, who might be armed. One inmate told me, "When you gonna rob somebody you don't know, it makes it harder because you don't know what to expect out of them." What if it were legal in America for adults to carry concealed weapons? I put that question to gun-control advocate Rev. Al Sharpton. His eyes opened wide, and he said, "We'd be living in a state of terror!" In fact, it was a trick question. Most states now have "right to carry" laws. And their people are not living in a state of terror. Not one of those states reported an upsurge in crime. Why? Because guns are used more than twice as often defensively as criminally. When armed men broke into Susan Gonzalez' house and shot her, she grabbed her husband's gun and started firing. "I figured if I could shoot one of them, even if we both died, someone would know who had been in my home." She killed one of the intruders. She lived. Studies on defensive use of guns find this kind of thing happens at least 700,000 times a year. And there's another myth, with a special risk of its own. The myth has it that the Supreme Court, in a case called United States v. Miller, interpreted the Second Amendment -- "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed" -- as conferring a special privilege on the National Guard, and not as affirming an individual right. In fact, what the court held is only that the right to bear arms doesn't mean Congress can't prohibit certain kinds of guns that aren't necessary for the common defense. Interestingly, federal law still says every able-bodied American man from 17 to 44 is a member of the United States militia. What's the special risk? As Alex Kozinski, a federal appeals judge and an immigrant from Eastern Europe, warned in 2003, "the simple truth -- born of experience -- is that tyranny thrives best where government need not fear the wrath of an armed people." "The prospect of tyranny may not grab the headlines the way vivid stories of gun crime routinely do," Judge Kozinski noted. "But few saw the Third Reich coming until it was too late. The Second Amendment is a doomsday provision, one designed for those exceptionally rare circumstances where all other rights have failed -- where the government refuses to stand for reelection and silences those who protest; where courts have lost the courage to oppose, or can find no one to enforce their decrees. However improbable these contingencies may seem today, facing them unprepared is a mistake a free people get to make only once." Award-winning news correspondent John Stossel is co-anchor of ABC News "20/20" and author of "Give Me a Break."