First: There is no doubt that the existence of some 260 million guns (of which perhaps 60 million are handguns) increases the death rate in this country. We do not have drive-by poisonings or drive-by knifings, but we do have drive-by shootings. Easy access to guns makes deadly violence more common in drug deals, gang fights and street corner brawls.

However, there is no way to extinguish this supply of guns. It would be constitutionally suspect and politically impossible to confiscate hundreds of millions of weapons. You can declare a place gun-free, as Virginia Tech had done, and guns will still be brought there.

If we want to guess by how much the U.S. murder rate would fall if civilians had no guns, we should begin by realizing — as criminologists Franklin Zimring and Gordon Hawkins have shown — that the non-gun homicide rate in this country is three times higher than the non-gun homicide rate in England. For historical and cultural reasons, Americans are a more violent people than the English, even when they can't use a gun. This fact sets a floor below which the murder rate won't be reduced even if, by some constitutional or political miracle, we became gun-free.

It's also important to note that guns play an important role in selfdefense. Estimates differ as to how common this is, but the numbers are not trivial. Somewhere between 100,000 and more than 2 million cases of self-defense occur every year.

There are many compelling cases. In one Mississippi high school, an armed administrator apprehended a school shooter. In a Pennsylvania high school, an armed merchant prevented further deaths. Would an armed teacher have prevented some of the deaths at Virginia Tech? We cannot know, but it is not unlikely.