Could an armed citizenry stop a terrorist AK-47 attack?

I’m not sure we’ll ever find out.
I would have been very interested if Mayor Richard M. “No Guns” Daley had a security meeting with Chief of Police Jody Weis after the Mumbai attacks last week. “How can we protect the people of Chicago from such an attack?” One or two years ago, I read a magazine article that suggested several inexpensive soft-target attacks in the U.S. One was launching a heat-seeking missile from a Southern California beach at a passenger aircraft on its takeoff path. Another was the kidnap and murder of a congressman. Two more were detonating bombs aboard approaching ships near New York Harbor and the Houston refineries. The fifth was an automatic-weapon attack by multiple terrorists at a crowded shopping mall in December, with a bomb timed to detonate at the loading dock right about the time the SWAT team would show up.
It’s the last one that most concerns me. Unlike another terrorism-prone country, we don’t have metal detectors at shopping-mall entrances. (They would come after an attack.) How to stop an attack once it is in progress? It only takes a few minutes—often less time than emergency response takes to show up—to inflict high numbers of casualties. A terrorist group would be far less likely to plan an attack on civilians whom they know are likely to be armed, and vice versa. That increases the probability of an attack within the City of Chicago. In Texas, where law-abiding citizens can legally pack heat, I imagine terrorists would be concerned about being shot and take their murderous plans elsewhere.
I never thought I’d say anything complimentary about Texas.