Some of the people here are missing the point.
It is not necessary to print the ENTIRE gun on a 3-D plastic printer. You only have to print the controlled part — the receiver. In some cases (such as the AR-15) you can buy the upper without government oversight. In addition, in some cases (such as the AR-15), the lower has to withstand very little force. The bolt (steel) locks directly into the barrel (also steel) while firing. The lower only has to hold everything together during recoil. Some force, but not nearly as much as the barrel and bolt see.
I would imagine that a LOT of other designs could be created that would have very little stress on the controlled part (the lower). This looks VERY interesting.
True, from a current legal standpoint. Print an AR15 lower receiver, which does little more than hold the remaining major components together, and most of it legally amounts to mail-ordering accessories.
Nonetheless, being able to insert bulk raw material & push one button and have the entire functional product appear is a major paradigm shift.