Soon after the Isla Vista mass shooting, an e-mail from Breitbart News, one of the slicker right-wing Web sites, popped into my inbox. Considering the source, the breathless subject line was startling: THE WORLD’S FIRST SMART RIFLE – NOW IN SEMI-AUTO A smart gun, as you probably know, is one that can be fired only by an authorized person, such as the weapon’s legal owner. Anyway, that’s the usual meaning. The way a smart gun works, smartplanet.com explains, “is that the gun’s biometric system is set up to recognize the rightful user through a unique identity marker such as a person’s fingerprint, magnetic rings, RFID chips or other proximity devices.”