You remind me a little of Bill Gates -- in one particular way. Remember when Bill said that there was no reason why anybody would ever want/need a computer at home? Even someone as intimately involved with computers as Gates failed to comprehend the universality of the computer age which he was instrumental in ushering in.
Well, I'm not saying that people will necessarily want or need 3-D printers at home. But the industrial uses are unlimited. Did you see the movie, "Skyfall?" The Aston Martin they destroyed was actually a product of 3-D printing which was created by Dassault Systemes -- a French company. You get why it was cheaper to destroy a inexpensive, modern fabrication as opposed to a classic Aston Martin? Good.
3-D printing allows the creation of much more precise instruments such as surgical tools than the current manufacturing -- and ultimately much more inexpensively. Also in the category of medical use, there is a patient which an entire new jaw which was created using 3-D manufacturing.
Dassault has contracts with aircraft manufacturers to create parts through its 3-D printing process . . . and in fact did create some parts for the new Dreamliner.
Lastly, and probably more significantly of all, there is serious work in progress at the elite universities with renowned science departments which will ultimately allow organs for human transplantation to be created via 3-D. Scientists are already growing tissue in the lab for such purposes as skin grafts. There is absolutely no reason that a kidney couldn't be created via 3-D -- and this is exactly the type of thing scientists are anticipating and working feverishly toward.
I'm not trying to persuade you, but rather just to educate you. I just bought Dassalt as well as DDD and one other 3-D company. Hey; if you don't like the prospects for 3-D printing, don't invest. Many, many, many other (smart) people will. It WILL be the next world-changing technology. And it WILL make investors rich in the same way that Apple and Microsoft made investors rich. This will happen whether you invest or not.