For one, printing something like that will likely result in it not working well. In one video (which is linked in that article), the gun managed to fire six shots before it fell apart where it was connected with a printed part. Not only that, but a 3D printer isn't exactly cheap. Anyway, I'm not worried about it. I'm all for banning [i]automatic[/i] weapons (as we don't need to have machine guns), but banning anything that has something that is militarized is a little silly when the base product can be purchased and just as easily used. Not only that, but those high-power weapons aren't even the most commonly used weapons in crimes, it's usually handguns. I don't think, at this point in time, 3D printing will allow for guns to work all that well (as that video I mentioned plainly shows). Later on it may do so, but at that point in time you also have to get the materials, models, and everything else, as well as assemble it, which means that the time to do it is outrageous. By the time something like that is feasible, we'll probably have a solution. If not, well, I'm sure we'll come up with one. Edit: Video I mentioned is embedded.