3D Printing represents huge potential for "creative destruction". Just imagine the industries that will be impacted if these things become commonplace. Forget about printing guns, these things represent an existential threat for a huge chunk of the manufacturing industry.
As such, I see our wonderful government with their backwards ivory tower solution being lobbied by the very industries these things threaten to put limitations on them. Unfortunately, once the genie is out of the bottle it's almost impossible to put back in. While the music industry successfully killed Napster, they had to admit that they couldn't keep making money off selling whole albumns on physical formats only. There is probably money to be made in 3D printing, but instead of finding those venues it will be fought tooth and nail.
While I'm sure there will be much fury over the ability to "print" guns what many people will not get is how worthless much of our gun control laws really are. Sadly, I doubt this will lead to a true meaningful debate that we really need to have about gun ownership and about repealing pointless laws (SBR's anyone?) while taking a hard look at causes of violence (War on Drugs)
"For every problem there is always a solution that is simple, obvious, and wrong." - Mark Twain