wizdum:
So we're probably going to end up in the same situation we have with copyright infringement? Where the government is saying "you have to stop this!" And the printing companies are saying "we'd have to hire 400,000 new employees to personally inspect each part".
Some things are apparent the moment you bring the 3D image up on-screen. They have to do more than that just to check that the file submitted can be made. See what that costs, it may be part of a set-up or engineering fee. A cam or cog won't stand out but a receiver with handle sure will.
Say you have a company that makes 3D printed parts and you know that if a part that you sold was found a fundamental part of a gun used in a crime that you could lose the company and go to jail, wouldn't you be extra careful about making just anything?
What I see probably happening is Big Business absorbing all but hobby 3D printing into a controlled industry.