An interesting philosophical discussion about this has recently occurred in my household.

We saw the video where someone had 3D-printed the "reciever" portion of a machine gun (the part of the gun that is legally considered the "gun", as opposed to the other parts that attach to it like handle and barrel) and it was able to get off several rounds before failing.

We came to the conclusion that, for those of us who want stricter gun control, we're quickly approaching an era where that point will become moot, and what we really should be asking for is bullet control. Bullets are harder to make, and won't be 3D-printed any time soon. (I mean, consistent, accurate, and deadly bullets are harder to make from scratch. I mean, any ball bearing can be turned into a bullet, but the gun that fires it isn't exactly the kind of thing that would be used to commit crimes frequently.)