Three of the horsemen of the cryptocalypse are resolving in our futurescopes. Their names are: the internet, Bitcoin, and 3D printing. Comms, money, and guns. The tools to win any war. Their substantial non-infringing uses render them unstoppable. Printed guns are clearly the most dangerous of the three for the general citizen. How do you stop children and the insane from mass producing them in their basements?
Close your eyes and hope that ABS plastic limits their utility? 3D printers are only going to get better; it's a matter of time before they can build objects out of metal. And a one-shot plastic gun is deadly enough.
Ban or regulate 3D printing? Hasn't worked out so far for any other kind of distributed technology.
Frankly, guns are just the thin end of the wedge. Downloadable home-brewable nerve gas is probably not far away.
Fortunately or otherwise, the fourth horseman is on its way: and its name is the final, total end of privacy in public spaces. 24/7/365 sousveillance of every space, and deep data mining of the result will be touted as the final, least undesirable, solution to keeping a lid on society's malcontents. It won't be quite enough, but the non-sousveillance applications (photography, evidence generation, personal safety) will be compelling enough to ensure it cannot be stopped.
And I for one welcome our transparent underlords.