Guns, like cannabis and "drug paraphernalia", are objects that are innocuous in and of themselves. Also like cannabis and the tools used to consume it, guns are typically used in a responsible manner, and, when misused, harm a very small percentage of the population. There are over 100 million gun owners and nearly 300 million guns in the United States, yet this country sees less than 1 million gun-related crimes and less than 10,000 gun-related homicides annually.
There's no reason to believe that 3D-printed guns would be used for harm at a rate higher than that of guns manufactured by licensed firearm companies. Therefore, it would seem that Washington would have ulterior motives for banning them and the technology used to create them, just like it has ulterior motives for banning marijuana and the tools used to consume it. In addition to limiting the public's relative firepower, the federal government has likely been pressured by business interests to prevent the populace from manufacturing its own firearms.
Anyone with a modicum of understanding of federal marijuana prohibition knows that Washington continues to ban the possession of the innocuous cannabis plant and the tools used to consume it primarily at the behest of "Big Pharma". It would therefore stand to reason that the federal government has banned the possession of the innocuous 3D printed gun and the technology used to manufacture it at the behest of "Big Firearm". After all, the American firearm industry, like the American pharmaceutical industry, is worth several tens of billions of dollars and has a very power lobbying presence in Washington.
Fortunately, circumventing this ban will be as easy as circumventing Uncle Sam's prohibition of pot. 3D-printed firearm technology--and thus 3D-printed guns--will remain as ready-accessible as marijuana and the tools used to consume it. In fact, in less than a day, you could locate and download the software, pick up the printer and media from the local office supply store, and print yourself an illegal firearm. Washington's ban of the innocuous 3-D printed gun will as prove futile as its ban of the innocuous cannabis plant.