This is not about a plastic guns, this is about a paradigm shift that is no less momentous than VHS and later MP3s.
I am not so sure about that. 3D printing has the potential to become a very important technology, but right now, printing cheap plastic trinkets is not what I would call game-changing. But that's just me: it just strikes me as a seemingly good idea - a little bit like flying cars - that can go both ways. It can be truly revolutionary (Crete your own factory in your garage! Let a thousand entrepreneurs bloom!) or it can be the kind of thing that never really lived up to its promise. Time will tell.
And another thing: whether the printed plastic gun really is unsafe or not, I believe it illustrates the risks of 3D-printing. In other words, if you really know what you are doing and printing to specs, using equivalent or better materials than the original creator, it's great. Or you can make a complete fool of yourself, and just print it, because, well, you can! And find yourself severely maimed - or worse - because you did not check the 3D file or whatnot.
On the other hand, the next time some idiot decides to rob a bank or convenience store with a printed plastic gun, the results could be highly amusing. I can see the TV announcements from here: "Another redneck gun-toting moron gets face full of lead and melted plastic. Film at 11".
As an aside: what's with Americans and their guns? Sheesh, people, grow up. You don't need a plastic-or-metal penis to be a real man. (And let the flame wars begin!)