There is some appeal to criminals, because the frame is the part that gets the serial number and is regulated. But if you want to attack this problem, the 3d printer is a backwards way to do it.
Isn't the same thing true for 3D printers? The first time someone tries to print something they frequently end up with spaghetti and less technically competent people wouldn't even be able to get the thing to attempt printing anything.
Separately, I am always a little confused by the idea that you cannot "trace" these firearms. Maybe people do not widely understand what's going on here, but the serial number being traced is on this lower receiver, which can be swapped out (in most but not all cases). If a firearm with a 3D printed lower is used in a crime, I have to assume - though I am not an expert - that you could still connect spent casings to that weapon in the same manner. In other words, it does not matter that the lower doesn't have a factory-installed serial number plate or a stamped serial number. My guess is that this confusion is being injected intentionally in the debate by the people who support/push these badly constructed laws.
It's presumably a misunderstanding of how investigations work. They're paperwork people so the assumption is that the serial number is of vital importance because it's what's on the paperwork, and if something could exist with no serial number then the entire system is in danger.
Meanwhile the serial number is overall not even that helpful. If you catch the suspect with the weapon in their possession then it doesn't matter that much what the serial number is, what matters is if the weapon they had matches the forensics. By contrast, if you don't recover the weapon then you don't have the serial number anyway.
The only case where a serial number would really do anything is if you recover the weapon after the perpetrator already tried to dispose of it and want to try to use the serial number to identify the original owner. But in that case the perpetrator can leave you without a serial number regardless by just filing it off. It doesn't really buy them anything for it to have never had one to begin with.
It was 13 years ago that the first major fully 3D printed firearm was released and even the ATF admitted that most of their reproduction attempts were capable of firing bullets at lethal velocities https://arstechnica.com/tech-policy/2013/11/feds-get-in-on-3...
I’m not an expert but even back then they could supposedly get 8-10 shots out of them.
So the claim that dozens of milled metal parts are necessary doesn’t appear to be factual
The barrel is so short and non existent that it basically does nothing except hold the (metal) cartridge in place. A liberator isn’t much different than simply holding a cartridge in a fixture and hitting it with a hammer.
In a conventional gun, the barrel serves to allow the projectile to build velocity and stabilize the trajectory by putting a spin on it. The liberator does neither, so the projectile will be moving quite slow and will be inaccurate.
And also, they do commonly explode, even on the first shot. It’s a gamble.
“Lethal velocities” doesn’t really mean much. A slingshot can propel a bullet at lethal velocities. And that would probably be a more suitable option for criminals as it would be more reliable and have more rapid fire capability.
Now it might be a viable one-shot gamble for a criminal in a place where guns are entire forbidden. But in those places, it is typically not easy to get a real .380 cartridge, so it doesn’t really change much. And in the US, there are much easier ways for criminals to get much better guns.