This defense argument is an excellent point.

Some observers believe the Virigina Tech Massacre is one example of why gun control is the wrong way to go when preventing crime. The ironic conclusion was first powerfully promoted in John Lott's study entitled "More Guns, Less Crime."

Lott wondered whether allowing people to cary concealed handguns deterred violent crime. He believed that if criminals weren't entirely sure who had guns to fight back and who didn't, they would be far less cavalier in their aggresive criminal attempts.

Believe it or not, his study of all 3054 U.S. counties from 1977 to 1996 bore his theory out. Although gun ownership rose from 27.4% in 1988 to 37% by 1996, crime rates fell. And the states with the greatest decrease in crime rates were the ones with the fastest increases in gun ownership.

The Western Standard's article, "Bulletproofing Canada" (May 21, 2007), reports,

According to Lott, for each additional year that laws allowing people to carry concealed handguns were on the books, robberies declined by two per cent, rapes by two per cent and murders by three per cent. If all states that did not permit carrying concealed handguns had allowed them in 1992, for instance, there would have been 1,839 fewer murders, 3727 rapes and 10,990 aggravated assaults.

School shootings also back up this theory. Lott looked at the eight public-school shootings between 1997 and 2000. In two of these cases--Pearl, Miss., and Edinboro, Pa.--the attacks were stopped by citizens with guns. Lott also examined all multiple-victim public shootings in the U.S. between 1977 and 1995. During this time 14 states adopted right-to-carry gun laws, and the number of such shootings declined by 84%, with deaths in the shootings reduced by 90%.

The Western Standard concludes,

It is sadly ironic that the Virginia Tech story might have been different if a bill to prohibit so-called "gun-free zones," such as the one at Virginia Tech, had passed the Virginia General Assembly last year. That legislation was drafted to prevent state universities like Virginia Tech from prohibiting students with concealed handgun permits from carrying guns on campus.

Murderers bent on a rampage care nothing about the law. But many citizens who could prevent them do. The best gun control is often control by guns, not control of them. It's why after doing his study, Lott bought a gun.