The guy who made the printed gun is a licensed firearms manufacturer, registered with and licensed by the Federal Government to manufacture and sell guns and gun parts, exactly the same as any other manufacturer with the same license. How he made the gun is immaterial, and the mere fact that he did it the hard way at ridiculous expense, and made a product so obviously inferior that most rational people would consider it more of a bad toy than a functional device does not affect that he did it according to the applicable US Federal laws.

If there is a concern elsewhere, it would seem more appropriate for those who have such concerns to voice them, and explain why they're frightened, than for those in the US to attempt to imagine what those concerns might be.

Those elsewhere may have difficulties with understanding our tolerance for people who do dumb things, but we generally prefer to prohibit only the things that are actually and demonstrably harmful to others. It's one of the things that makes us such "good neighbors" in the international community - and so dearly loved by the whole world.

John