Well, the other question is whether it will be legal to manufacture/sell printers which are capable of printing illegal things. If the printers are capable of s

Well, the other question is whether it will be legal to manufacture/sell printers which are capable of printing illegal things. If the printers are capable of self-replicating it will be implausible to enforce that sort of regulation. It is presumably already illegal to 3-D print several types of 3-D things, where such things themselves are illegal or where there is some form of copyright, trademark or patent infringement.