It has happened: A legal ban on digital DIY files
A milestone in DiDIY history: The Australian police has (very likely :) been reading up on our work about ethics and the New South Wales Parliament decided to ban not certain objects, but certain digital files! http://3dprint.com/106940/australia-ban-3d-files-guns/
"The NSW police department actually obtained 3D printing equipment and made two firearms of their own. They were, not surprisingly, shocked at being able to make weapons so expediently and affordably."
The decided the danger is not in the physical object, but in the digital description. That's a first!