With any luck 3d printers will become more ubiquitous in the next few years, and this will all clearly be no longer the case.
3d printers that people can afford can only produce garbage guns. 3d printers that professionals use (i.e., that cost tends of thousands of dollars) can produce slightly less crappy guns. In either case, you end up with a product that is substantially lower quality that mass-manufactured equivalents and costs substantially more.
What kind of idiot would pay more money for a lower quality product that could easily blow up in your hand severely injuring you? I mean, it is not like there's a shortage of mass-manufactured firearms.
Sure, ABS plastic weapons are still somewhat laughable. What happens when you can print a metal gun in your own home with some metal powder, with a machine purchased for less than $1K?
Note: Boeing uses laser sintered parts in their new Dreamliner; this isn't just for prototyping.
EDIT: Make Magazine plans for an open source laser sintering device: http://blog.makezine.com/2012/02/01/an-open-source-laser-sin...
What happens when I buy an eight-round Mossberg from the pawn shop for $250 dollars (that is like 8 Rasberry Pis!)?
Odds are, same outcome: it sits around doing nothing, because nearly nobody is murderer just itching for an easy way to do it.
The average citizen who wants a gun has one. And they have one that is much more effective than this 3D printed gun.
Anyways, no, I don't think that it will make a huge difference--the materials in use and the resolution in printing is just comical compared to even a simple throwaway zipgun.
https://en.wikipedia.org/wiki/Improvised_firearm