"Ghost Guns!

AAAAAARRGHHHH!"
Short version: Slate writer discovers it doesn't take a factory to make a gun.  And really doesn't like it.
Such cases are clearly just the beginning and threaten to sink reasonable efforts at regulating the traffic in “ghost guns,” as these weapons have been called. Unlike Japan, where strict gun laws prohibit even the private manufacture of deadly firearms, the United States allows most types of guns to be made at home provided they aren’t then sold or given away by their creators—hardly a disincentive to those already trading in the black market.
A: those already trading in the black market are already breaking laws, but that doesn't seem to matter, "THIS MUST BE CONTROLLED!" 
...Last year California Democratic Rep. Mike Honda introduced the Homemade Firearms Accountability Act, which would subject homemade guns to many of the same regulations as firearms sold commercially—though the bill stands virtually no chance of passage in a Republican Congress heavily beholden to the NRA and the gun lobby. Already in 2013 the Department of Homeland Security had issued an intelligence bulletin warning that halting or even slowing the distribution of the new homegrown guns “may be impossible.”
Guess what, Honda and Holsinger?
Which is what's driving these people nuts: the home-owned CNC mill isn't a new tech, just an advancement on old.  And the commoners can use it for things people like Honda don't approve of.

And we should note that, as reports from Australia and Brazil and other places have shown, bad guys have been making guns without fancy equipment for a looong time.

By the way, if the 'Rep. Honda' sounds familiar, that's because he also doesn't like the commoners owning body armor.

And let us not forget the idiot who started calling homemade firearms 'ghost guns', State Senator Kevin de Leon, also of Californicated.