Glenn Reynolds (Instapundit) is a professor of law at the University of Tennessee. He shoots straight in the NY Daily News:

Police can't be everywhere, and as incidents from Columbine to Virginia Tech demonstrate, by the time they show up at a mass shooting, it's usually too late. On the other hand, one group of people is, by definition, always on the scene: the victims. Only if they're armed, they may wind up not being victims at all.

"Gun-free zones" are premised on a fantasy: That murderers will follow rules, and that [legally-armed students] . . . are a greater danger to those around them than crazed killers like Cho Seung-hui. That's an insult. Sometimes, it's a deadly one.

'Nuff said.