Even with CNC programming, a person has to have skills to properly mount and orient the work (center if on a CNC lathe, zero the coordinate system if on a mill)

Even with CNC programming, a person has to have skills to properly mount and orient the work (center if on a CNC lathe, zero the coordinate system if on a mill), machine, and assemble. It takes decent skill to make a firearm with conventional machining. The concern (I'm not saying it's a founded concern) is that 3D printing would allow unskilled folks to download increasingly complex plans and implement them with little skill. The pool of people with good CNC machining skills (and access to at least $10K worth of very heavy equipment) is probably less than the pool of people with $5K spare cash (ballparking what a future 3D printer might cost) and only basic mechanical skills.