Public shootings have become a familiar American spectacle in recent years, and two more occurred in recent weeks. The details are still unfolding, but so far these episodes seem to fit the general pattern. At Los Angeles International Airport, a young man entered a public area and started firing. Three days later, in the midst of intense media coverage of the first event, another young man did the same at a shopping mall in suburban New Jersey. One penned a note beforehand about his actions, the other a manifesto. Only the L.A. shooter appears to have meant to kill others, but both apparently planned to die in highly...