I understand the intent, but feel that there are so many other loopholes that put much worse weapons on the street than a printer. Besides, my prints can barely sustain normal use, much less a bullet being fired from them. I would think that this is more of a risk to the person holding the gun than who it's pointing at.
At that point though, you may as well start regulating the purchase of lumber, since it sounds like you could just as easily make the printed components in a basic workshop as with a 3d printer