This debate is somewhat similar to debates about religion or politics. Certainly, we can all agree that having harder to detect guns is not good for schools and airplanes. But legislating against 3d printed guns will be about as effective as legislating against drugs. It won't really affect availability. What we really need to be trying to fix is the root cause of the need for guns and drugs and that's poverty, disenfranchisement and lack of economic opportunity. The way to do it is to go ahead and outlaw 3d printed guns (well, all from my perspective) but don't spend billions trying to enforce the law so stringently because you'll never stem the flow. Instead, enforce the law at a reasonable level and redirect the majority of those saved funds into public assistance programs to ease the the burden on peoples lives that drive them to drugs and crime. You could spend the entire GNP of the US on enforcement and you'll still have plenty of drug and gun related offenses. Fix the cause, not the result.