The massacre of a dozen movie-goers in Colorado has sparked another spate of liberal demands for gun control. University of Colorado Professor Chad Kautzer has launched an online petition aimed at banning “concealed carry laws.” While acknowledging that such a ban might not have stopped James Holmes from shooting 70 people in an Aurora, Colorado movie theater, Kautzer insisted that “the ability to add an illegal possession of a firearm charge to the list of offenses for which he will be prosecuted would have a deterrent effect.” In New York City, Mayor Michael Bloomberg suggested that police should go on...