A debate is under way about how best to respond to North Korea’s cyberattack on Sony, an attack designed to punish the firm for making a movie that humiliated Supreme Leader Kim Jong Un. Ideas range from a cyberattack to weaken North Korean political and military assets to relisting the country as a state sponsor of terrorism, presumably accompanied by new sanctions.

These ideas are fine as far as they go, but they don’t go far enough. The serious threat posed by North Korea far transcends cyberspace. Only one approach is...