People have always been drawn to spectacles of violence. As Sissela Bok points out in her book Mayhem: Violence as Public Entertainment, the ancient Romans forced slaves and convicts to fight wild animals to the death before roaring crowds as a matter of public policy. “Violent spectacles kept the citizenry distracted, engaged, and entertained and . . . provided the continuing acculturation to violence needed by a warrior state.”

In comparison to the ancient Romans, modern Americans seem far less bloodthirsty. After all, writes Ray Surette, author of The Media and Criminal Justice Policy, “We do not kill real people in public spectacles.” Nevertheless, warns Surette, the level of fictional violence in American culture is staggering: “We have eased the access to fantasy slaughter far beyond anything the Romans dreamed of.”

According to researcher George Gerbner, “Never was a culture so filled with full-color...