Those of you that watch "Sons of Guns" might have seen the episode where they built a plastic "Zombie" gun platform with a 3D computer generated 'replicator'. Then they built in the steel parts.
Producing an 'all plastic' gun has already been done. It successfully fired several rds before it became unsafe. With readily available technology and soft ware, this isn't the stuff of movies, but real life. ANY 3D object can be replicated.
The point? Passing all the laws will NOT prevent people who can't get a gun any other way from building/making their own. Even if it self-destructs eventually, it can be used to capture a more functional weapon. Of course, you are then a "manufacturer" and answerable to the BATF, but if you're already a criminal, this won't keep you awake nights.
Remember the .45 ACP "Liberator" pistol of WWII? It was made of steel stampings and probably cost pennies to make. A collector pal has one and he has fired it - once! Recoil was memorable and it didn't ruin the gun.
Wood and plastic 'guns' of the James Bond spy genre have been out there for a long time, undetectable at airports if disassembled, ammo carried in simulated ball point pens, etc.