I spoke this morning with James Alan Fox, who said mass killings were not unknown in the U.S. prior to 1966 — when Charles Whitman took to the Texas tower with an arsenal and began picking off civilians — but they were exceedingly infrequent. Ever since 1976, we’ve been averaging more than 20 per year. Now, that has to do with a lot of things. It has to do with industrial-strength violence on TV and the movies, and the obsessive use of violent video games by young men, and the increasing mobility and atomization of society — but, as the Aurora shooting demonstrates, the carnage is greater (and the experience more otherworldly kinetic) when assault weapons are involved.