A gruesome holiday season exercise: Think of some firearms and accessories that might have added to the body counts of Aurora and Newtown. More starkly, imagine the means by which coming Auroras and Newtowns will be made more deadly.

The exercise starts with a militarized baseline, as both shooters unloaded designed-for-damage rounds from high-capacity magazines loaded into assault rifles. Improving their killing efficiency would require one of two things: the ability to shoot more bullets faster, or more time. A fully automatic machine gun would provide the first. More minutes to hunt, meanwhile, might be gained by employing a noise suppressor, those metallic tubes better known as silencers. By muffling the noise generated with every shot by sonic booms and gas release, a silencer would provide a new degree of intimacy for public mass murder, delaying by crucial seconds or minutes the moment when someone calls the police after overhearing strange bangs coming from Theater 4 or Classroom D. The same qualities that make silencers the accessory of choice for targeted assassination offer advantages to the armed psychopath set on indiscriminate mass murder.

It should surprise no one that the NRA has recently thrown its weight behind an industry campaign to deregulate […]