3d printing isnt shit except for ease of use. I can make a 12 gage slam fire shotgun in a couple hours with maybe $100 on a home depot or Lowes gift card. As a machinist and welder, I can make a whole lot more than that.
On the one hand, its moronic to think that limiting 3D printing will in any way affect ease of access to firearms. On the other hand, literally anything making it harder for people to kill or harm each other is probably for the best in the long run.
A comedian I watched a while back had a bit about if the government really wanted to stop gun violence, they’d put a massive tax on ready made ammunition. You really gotta hate a bitch to spend $5k on a bullet to kill them. Obviously this doesnt take into account making your own ammo, but the point stands.