I'm not a gun guy but from my understanding of ghost guns you pretty much buy the whole gun online in parts, and you just 3d print a handle.
So I don't understand why people are so afraid of 3d printing when it really has minimal to do with the final product. From what I can tell you can't just 3d print a gun from start to finish like its a llm. You still have to buy the actual gun parts from the manufacturer. To me this sounds completely unrelated and like a issue with regulating gun parts.
You can carve a handle out of soap, wood, or buy a solid chunk of plastic and its the same result.