The current copyright controversy is driven by the fact that duplicating an information artifact costs much, much less than purchasing said artifact. However, this effect is not present in 3D printing. The base material costs money, and the range of possible materials is restricted. Therefore, mass manufacturing of parts should still be cheaper, more efficient, and in some cases produce better products, than at-home 3D printing. These parameters may change as the technology matures, but I doubt the Chinese plastic trinket market is in danger anytime soon. Rapid prototyping is far more a means of creation than it is a means of production.
Most plastic objects we encounter day-to-day have little value added beyond their actual physical manufacturing cost. As long as mass production remains more efficient for plastic parts, there should be enough of a gap between the cost of home printing and the cost of an industrially produced item to discourage piracy. I understand that this is oversimplified : there may be objects that have artificially enforced scarcity, by copyright and patents. However, I just can't remember running into such an object, built only out of plastic, in recent memory. Design patents are still an issue, but these do not limit functional reproduction, only aesthetic.
I'm obviously overlooking some things. For instance, a 3D printer that could operate on recycled materials just might undercut mass production. However, there is still an upper limit to how much thermoplastic you want piling up in your house. If you had to physically print out every article you wanted to pirate, your study would rapidly fill with articles and papers ( and indeed, many of our office are such masses of papers ). At some point you'd realize that the cost of all that toner might not really be worth it.
Of course, you might get a situation where people pirate objects, print them, use them for a time, and then recycle them back into feedstock. But, what would have been the fate of the same objects had they come from industrial production ? Overwhelmingly, they would be destined, like so much of the rest of the 20th century, for our landfills,
garbage islands in the Pacific, and
the stomachs of (dead) albatrosses.
The only way rapid prototyping could become a sustained threat to manufacturing is for rapid prototyping to become both sustainable and a viable means of manufacturing, of which it is neither at this time.
I feel that there is some sort of intrinsic efficiency gain to mass production that will always discourage piracy of printable objects, but I would also love to be proved wrong in this assumption. If or when printing technology matures to this point, well ... heh ... they'll never be able to stop us anyway.
p.s. : but seriously, the paper is good and basically a completely accurate, way better analysis, than this post. so, head over there.