In the wake of horrific crimes like the recent mass shooting in Oregon, many in the political class respond as if there were an easy way to keep such tragedies from happening. If it weren’t for the stubbornness of the National Rifle Association, the story goes, these deadly incidents could be prevented. Democratic presidential frontrunner Hillary Clinton urged “sensible restraints,” and said if she is elected president she would use her executive authority to impose them.

This sort of rhetoric suggests that there is a workable...