Gun violence is caused, first and foremost, by the presence of a gun. A sufficient cause? Often yes, given appropriate context.
There are plenty of very successful ways to "hold back" this technology. It's called law.
Anyway I don't think anybody is worried about this 3d printed deal other than the press trying to get page views. The scrawny middle class kid who made it is an uninteresting attention whore, and the gun itself is a massive piece of shit. As others have pointed out, self-made ballistic weapons have been possible for years. This doesn't lower the convenience factor.