If we want to stop these mass killings, it’s time to ask where these massacres occur. Sandy Hook Elementary School, where all firearms are prohibited; Virginia Tech, where all firearms are prohibited; Aurora, Colo., where state-licensed concealed-carry firearms are prohibited, in a theater where all firearms are prohibited; Norway, where 69 youths in training for political leadership were killed on gun-free Utoya Island; Tucson, Ariz., at a meeting of Democrats who, as a class, favor gun control, think firearms possession is bad and, as the killer expected, were all unarmed. People who want to kill a lot of people go …