In March, Stephen Harper’s government reversed decades of increasing restrictions on civilian firearms, scrapping the controversial long-gun registry on grounds that it was wasteful and ineffective. Gun laws, the prime minister correctly said, should focus on criminals rather than law-abiding citizens such as farmers and hunters. Some claim that this Conservative policy flies in the face of a mountain of evidence, and even represents an assault against reason. Canadian voters seem divided on this issue, as well as some basic related questions: Are firearms in the hands of ordinary citizens a serious threat to public safety? Is registration an effective...