Here's the thing...

I can buy an AR lower without issue (the only part the gov't cares about).  I'm a good boy, and I pass the NICS check.  I can also now make one, buy an 80% kit or with a 3D printer.  Eventually, the price will be the same either way, and I'll just go with whichever is most convenient for me.  This is not a problem, the constabulary isn't really worried about me as they have many more bigger fish to fry and fret over.

But, with the 3D printers, nefarious types that are prohibitted persons will one day easily be able to do the same and not even have to be that clever to accomplish it.  The technology will be as if someone waved a magic wand and turned everyone into a master gunsmith.  A world of nothing but gunsmiths.

When that happens, we are back to 1969.  NICS checks will be nullified and bypassed.  It is up to the individual not to break the law, not the government to watch over him and approve or disapprove all prior-constraint like.  Which, I think is a good thing, but that the freedom loving libertarian in me.

But man, Hoplophobes aren't gonna like that at all when they grasp the ramifications.  They can't put the genie back in the bottle.  What WILL they try to go after instead to short circuit things?  Case primers are hard to make on your own.  Maybe they will regulate anything that has or is a primer.