Guns that can be 3-D printed exist today. They have been fired, and they work. They aren't dotting the American landscape just yet, but give it a few years and they well might be. Two problems exist with the potential for widely available 3-D printed guns. One of them is obvious (guns would be much easier to distribute and much arder to keep track of), the other is made clear by this commercial for the downloadable app that tells your 3-D printer how to make a gun called The Liberator:
Problem #2 with 3-D printed guns is who would want one and why. Gang members and other criminals would love to have a hard-to-trace gun, but that's not the target market here. Look at the messaging in this commercial: epic music, a sunrise, planes flying overhead, the name "The Liberator"...it's a modern version of war propaganda. And who is the war against? Our own government, of course. Second amendment fans claim that we need the second amendment in case the government turns fascist and we need to overthrow it. The government has planes, but now you, yes you can print your own guns. And Liberate us from this non-existent threat.
It's a veritable certainty that as soon as the 3-D printing market is viable in the U.S. economy, Congress will seek to regulate it, and gun advocates will kick and scream because the Democrats want to quell the revolution by taking away your 3-D printed guns. Many people dream of a revolution, and that revolution happens to look a lot like a movie preview.
Thing is, that's why Democracy is awesome: you can replace George W. Bush with Barack Obama without bloodshed. Want to replace Obama with Rand Paul? Great, all you have to do is get enough people to agree with that vision. If you can't, then what's your revolution about anyway?