If you’ve heard of “ghost guns,” you may have begun to panic about an epidemic of untraceable firearms lacking a federally-mandated serial number and assembled from parts purchased online or 3-D-printed. A recent New York Times article warned that ghost guns “can be ordered by gang members, felons and even children,” and deemed the rising number of seized ghost guns a “crisis.” The head of a gun-safety organization called ghost guns “the biggest threat in the country right now.” The problem? None of this language is new. It echoes 60-year-old rhetoric first used to describe the country’s original post-World War...