Over the past several years, there have been a number of incidents of mass shootings, at schools, at entertainment venues and so on. Immediately after these incidents, there is usually a call, by those who reason that fewer guns will result in fewer mass killings, to outlaw or greatly restrict gun ownership. This is usually countered with the argument that if law-abiding citizens don’t own guns, they will be defenseless against criminals who would possess them. A question tha