My piracy response was a little tongue in cheek, but the only really good answer to "why not just print it?"
3d scanning technology is also getting up to speed very quickly; this will make regulation impossible, and just create another direct parallel to the music industry.
I already own the CD, I bought it from the intellectual property owner, so why can't I make a copy of it for "personal use" in case the original is lost or damaged? What if I want to keep a copy in my car, and in my home?
Replace "CD" with any part that can be 3D printed, and let the games begin. Prices for parts will increase to make up the loss in market share (have to cover that overhead) and that will drive more consumers away. Then maybe Billy Bob down the street will print you a $100 part for $20.
If the value is in the labor/materials, then I will just make it myself, no harm no foul. But once the argument is made to assign the value of a physical object to the intellectual property it contains, quantity of the object becomes insignificant (from one side of the argument at least.) As long as I paid for that intellectual property once, I can make as many physical objects with it as I see fit (for personal use only, of course.)
I'm afraid the next big career boom may be in the legal profession... Why make something new when there are plenty of things out there to argue over?