.... Seriously?
People, I live in Australia, and right now I have a functioning musket sitting in my garage that I built from paper, cardboard, a shit ton of glue and some Peizo Ignitors with a friend. It just uses Armstrong Mixture for gunpower with a spark that sets off some rubbing alcohol, and there you go, a gun.
Now, if I were to take this and go shoot someone, not only would it be unlikely to even bruise them, but it would probably miss, mis-fire or just go balls-up. It's the kind of thing that you build just for the sake of having a kick-ass musket you can shoot a log with.
It's the same with these printers. Do you honestly think that someone can kill someone with that gun? Look at it, it took many tries to finally fire, and then the barrel broke. If you actually wanted to murder someone, it would be easier to just print out a fucking sharp plastic knife!
And please, dear lawd in dem heavens or whatever, stop saying "Soon" or "In the future". In just about every thread I see now, someone goes "There's nothing wrong with it... but in the future!" It is completely irrelevant. When they invented bombs, they were not worrying about atomic bombs. Yes, progress brings with it many things, but at the moment we have not progressed to the point where we can do all the things people are worring about. And besides, every time someone says "You can just print a real machine-gun!" think about how other tech has caught up. By the time we can do that, why the hell wouldn't we have full on laser guns? Or invulnerable mech-suits? etc. etc.
Just take this for what it is, some guy printing a barrel and a trigger and throwing some gunpowder in there to watch it go boom.