There is a little quasi-statistical mystery deep inside the gun-control debate, but no one ever seems to mention it. We say, ban the guns that kill our children. The gun lobby says, relax gun laws so that we can arm the good guys; "the only thing that can stop a bad guy with a gun is a good guy with a gun."

According to Mother Jones magazine, in the 62 mass shootings that have occurred in the United States during the past 30 years, never — not once — has an armed civilian halted an attack by firing on a perpetrator. Oddly, Mother Jones did not ask the logical follow-up questions: Why not? Was no one carrying a gun ever present at one of these shootings? That seems unlikely. And yet both sides of the gun-control debate seem to be operating on the premise that people have not already been carrying guns in places where mass shootings happen. Both common sense and my own personal experience as a criminal lawyer belie that assumption.