Gun Control's MP3 Moment
Reading the continued, ongoing arguments about gun regulations ("reasonable" or otherwise) is frustrating. Not only for the usual reasons (absolutist positions, inability to recognize multi-causal phenomena, relentless hostility towards different opinions, etc.), but because of how incredibly irrelevant it is becoming. 3D-printable firearms are already here, and becoming increasingly reliable. Every gun control law in the world is obsolete.
With a 3D printer costing a thousand dollars or less, it's possible to produce a usable firearm. The first generation of these printed guns had a tendency to blow up when used, but the newer models can work just fine. Single-shot, magazine-fed, automatic or semi-automatic, there's now a variety of weapon designs available, ready to be downloaded and printed out.
Controlling this won't ever be easy, and is currently impossible. The design files are digital and easily spread around the Internet. 3D printers are general purpose systems, meaning that they can ostensibly be instructed to print out anything possible (given their size and material resource limits). Printers may be programmed to recognize a specific 3D gun file, but aren't smart enough to identify any random file that will produce a weapon. Open sourced 3D printer designs would make it possible to avoid the use of devices programmed with ORM ("object rights management") restrictions. You're not going to arm a militia with one of these, at least not quickly, but it wouldn't be hard to print out a small arsenal for person enjoyment.
Again, this is stuff that's happening now. It's not easy, quick, or cheap at the moment, but it's heading that direction. I'd be surprised if we didn't see someone killed with a 3D printed weapon by the end of the decade. Continuing to fight over gun control laws is painfully close to the music industry continuing to demand "home taping" restrictions and taxes on cassette tapes, even as MP3 files proliferated.
One final caveat: A 3D-printable firearm still needs ammunition, and bullets will be hard to 3D print for awhile yet. It may be another decade or more before it's possible to easily print bullets. If we really want to continue the debate and hostility, we may have a few years left.