According to the hype, 3D printers are going to change the world in many positive ways. For example, home 3D printers will allow people to create replacement parts when something breaks. As another example, home 3D printers will allow anyone (with the money) to create their own objects (although much of this will be plastic junk). As a third example, the fact that 3D printers are almost universal machines (that is, they can theoretically make almost anything) will allow cheaper manufacturing. Not surprisingly, there is also a dark side to 3D printing.
One obvious point of moral concern is that such printers can allow people to print their own weapons and use these to harm people. While the first printed gun is not much of a weapon (it essentially a plastic “zip gun”), it did show that guns can be printed using the current technology. As the technology improves, it seems reasonable to believe that much better weapons could be printed, thus allowing the usual suspects (criminals, terrorists, and so on) to secretly print up their own weapons.
While this is a concern, people can and do already make their own weapons. While these weapons are usually fairly crude, they can be quite deadly—as the Boston Marathon bombing of 2013 showed. As such, 3D printing would not seem to significantly increase this sort of threat.
People can also get the metalworking tools needed to make more sophisticated weapons, although these are rather expensive and require skill to operate. Because of this, 3D printing might present an actual threat—a person does not need any special skills to print up a gun, although a printer capable of making an effective gun would probably be rather expensive.
Overall, until the printer technology is cheap and effective enough to print effective guns (that is, comparable to manufactured firearms), they will not present a significant threat. As such, there seems to be (as of now) little moral reason to be worried about this sort of use of 3D printing.
Another matter of obvious moral concern is that 3D printers will allow people to easily and secretly duplicate patented and copyrighted objects. Using a currently available home 3D printer, a person could print up copies of toys, miniatures (for games like D&D), parts and so on. Thus, 3D printing will allow people to do with objects what they have been doing with music, movies and software, namely engaging in piracy.
“Solid piracy” or “3D piracy” does differ from digital piracy in at least one key respect. In the case of printing an object, a person is not stealing the physical object that the manufacturer made. For example, if I were to print a copy of a copyrighted dragon (or gargoyle) miniature for my Pathfinder game, this is rather different from me going to the local gaming store and shoplifting that miniature.
On the one hand, this does seem to be a meaningful difference: by printing the dragon, I am not actually stealing the object. After all, no one is deprived of the object. As such, copying and printing a patented or copyrighted object would not be theft in the usual sense of stealing an actual object. Similar arguments have, of course, been given as to why pirating software, movies and music is not theft.
On the other hand, this does still seem to be theft. While I am not guilty of stealing the matter that makes up my dragon (assuming I did not steal that) I did steal the design of the dragon. For something like a plastic dragon miniature, the matter that makes it up is not the valuable component. Rather, to go with Aristotle, it is the form of the matter. In this case, the form of an imaginary dragon.
This sort of theft of design is nothing new—people have been stealing designs and producing their own objects for quite some time. What is different about 3D printing is that it makes such theft of form very easy. Sticking with my dragon example, before 3D printing it would have been very difficult for me to steal the dragon design/form: I would have had to create a mold of the dragon, melted down the plastic to make it and so on. It would, obviously, be cheaper and easier to just buy the dragon. However, 3D printing would allow me to easily copy the dragon. While there would be the cost of the printer (and perhaps a 3D scanner) and the materials, if I did enough copying and the material was cheap enough, it would also be cheaper to steal the dragon design than buy the dragon.
However, it would still be theft—I would be using the design owned by someone else without providing just compensation and this would be just as wrong as stealing a movie, software or music. Of course, there are those who contend that copying movies, software or music is not theft and they would presumably hold the same view about solid/3D piracy.