[Juan Loco]

Two things.
Firstly, on the 3D printing side of things, yes its extraordinary, however like a lot of things it comes down to budget. There are some cheaper units out there, but realistically they are novelty value only, as the end result is very rough.
Keep in mind that the greatest benefit of this technology is prototyping. The ability to transform a computer design into a working model without any intermediate steps.
For metal though, I suppose some very intricate "pre-assembled" designs are possible but for the most part I feel CNC is superior.

Now onto the plastic guns nonsense.
Any idiot can make a gun. (How well and reliably it works is a different matter.)
The difficult thing (in Australia) remains sourcing the ammunition.
NO plastic breach could contain a modern high pressure cartridge. At best you might get off one very dodgy shot, at worst the thing will literally blow up in your face. You can get a better result with a toy gun and some piping.
And here's the big thing: Criminals have access to guns. If you're a crim and need a gun you can simply buy one, or better yet steal it.

The big danger, when these printers become more common, is that some kid will get hold of some ammo from their dad, "print" themselves off a "gun" and blow their fingers off.