I think you have some blinders on. While this story is about 3D printed guns that is too narrow minded. You can't do anything with a 3D printing you can't do with a milling machine.

Mills do cost more, regarding IP it is very similar these days with CAD. You can mill parts from plastic, aluminum, Ti or Steel.

I can't advocate for the libertarian view that there should be no restrictions on possession or ownership of weapons. Weapons need to be regulated the issue is more about where you draw the lines on who and what. Should anyone be allowed to have RPG's. If you decide the line should be drawn at explosives what about hypervelociy tube launched rockets. If you say no rockets, what about hobbyists. Are you aware of LDRS, have you seen their toys.

https://www.uroc.org/content.aspx?page_id=22&club_id=591702&module_id=365434

Explosives/fireworks are regulated but not really more than firearms. Just different infringements.

Lasers, seems to becoming an issue, how about rail guns. Is a rail gun just an electric catapult and completely unregulated.

I think we need regulations but then again, I don't think Congress could pass common sense regulation or enforce it properly.

TEK