The fuss about 3D printing of firearms has been invented by the media to generate artificial drama, demonize firearms, and sell advertising. Nothing more.
You're leaving out the originators of the fuss. Various childishly foolish individuals doing the Utube/social media equivalent of thumbing their nose at the govt, chanting "neener, neener, I can make a gun you don't know about!!"
I think the undetectable firearm is a real concern for homeland security . It really will only take one more step to figure out how to make them and they not blow up .
Undetectable anything is a concern for homeland security. As far as not blowing up? Already done, you just need to use material strong enough to withstand the pressure.
An intriguing fictional account can be found in the movie
In The Line Of Fire, where the bad guy casts a non metal gun from resin. NOT 3D printed, cast in home made molds on the kitchen table.
The gun is double barrel, and fires what appears to be the .38 S&W round. However, the bad guy has to use conventional ammunition, which he gets past the metal detector by putting the 2 rounds inside a hollow "rabbit's foot" fob on his keyring (which does NOT go through the detector).
It is entirely plausible that the right resin could be strong enough, when thick enough (the movie gun was very "clunky" much thicker than metal would need to be) to survive multiple firing of a low pressure round like the .38S&W.
If I understood it right, the whole flap over the Defense Distributed gun wasn't over the gun itself but over the intellectual property (plans/printer code), its distribution, and court rulings concerned with that.