Well I don't worry about anything...but that aside I don't see any need to worry about printing weapons. There are so many easier and inexpensive ways to get real working weapons instead of trying to fabricate and then have to test whatever you get out of a 3d printer. I'd also think you'd need a much more costly printer to print out of material suitable for such a device.
Actually, the idea of making weapons with a 3D printer is more MHO than OHM considering the rise in gun sales and sold out ammo shelves. Cars run wild, planes fall from the sky, electricity burns homes, chemicals in food and "medicines" kill by the thousands - slowly, knives slip, words destroy, shut ins and agoraphobics fall out of bed and break their necks. So. . . ? New technology breeds new risks. Always. We will probably figure out the right thing to after we exhaust all the wrong ways first.
There are lots of things to worry about, I think this growing segment will continue especially in these early stages, the stock will retrace at some point but we ahve'nt seen anything yet as far as where this is headed in the next year or two. There is a huge short interest currently and if SSYS and XONE show equivelant growth we will see 50 before 30's IMHO