I don’t see how a printed gun would be strong enough to hold the pressure of modern rounds with smokeless powder.
It is cognitive dissonance.
Anti-gun types know guns cannot be made at home.
Someone shows them, in a way they understand, that they can be made at home.
Cognitive dissonance happens.
Guns have been made at home for centuries.
The designer in this case has a YouTube video to show you, and the reality is the materials science is only going to get better and better.
You can make a weapon that will last longer with a piece if wood,a section of antenna,a nail and rubber band.