Why putting armed citizens at schools is a stupid idea

From a Bloomberg News story that had nothing whatever to do about firearms:

"After being dismissed from her job as a Midtown Manhattan securities attorney in October 2009, Christina Tretter-Herriger hitched a used horse trailer to her Dodge Ram pickup and drove 1,628 miles to Texas.

"The 32-year-old lawyer sold skin-care products in Houston before finding work as the assistant general counsel of a futures-trading firm where an irate customer punctuated a recorded voice-mail message with gunfire."