it comes down to unreasonable fear and emotionalism, which is difficult to counter with logic, because they won't listen to reality.
Which pretty much fits every gun control measure in the past 100+ years...
3D printers are the new bugbear in the woods, but I don't think the landscape has changed as much as the ability to get around in it has.
with one of these, you don't have to be (or hire) a skilled machinist, you just have to have and run the program.
I can, right off the top of my head, think of several things (not necessarily practical or even workable, but that should be no barrier to our politicians, based on past performance...) that could have an effect on the "danger" of "undetectable" guns..
Better metal detectors....
requiring every 3D printer to send a picture/file of what it makes to some central govt agency computer....
Requiring all passengers to travel nude....
passing a law that says killing someone is a bad thing....
comprehensive background checks before allowing passengers to board public transportation...
comprehensive background checks before allowing ...purchase of a 3D printer,
not allowing people to possess fire, because it burns....
I think you get the picture...
The risk is in the details of whatever law or regulations they craft to deal with the danger of the undetectable gun. What features they use to define it. Remember the fine things the GCA 68 did for us, defining
acceptable guns by a point system designed by some bureaucrat.
I hear some moron is wanting to ban plastic magazines, because (supposedly) they are "undetectable". Amazing....