[gmueckl]

But money counterfeiting is a different proposition: the printer is blocking exactly known patterns found on real currency. In fact, many bill designs incorporate patterns that are easily machine detectable for this purpose.

Blocking the printing of parts of mechanisms is a completely different beast, because the functionality is only discernible after final assembly of the individual parts, which can be shaped in a variety of ways. Most of these parts are unique to guns or at least usable in other kinds of designs. E.g. the same trigger lever design could be used for a ghost gun or a nerf gun or a water pistol. So where would yiu draw the line of all the classifier sees is G code that combines support structures, the actual surfaces and infill of some arbitrary collection of parts?

I'm against guns in generally, but this classification problem seems particularly ill posed and I don't want it to result in tamper-resistant printers stopping people from tinkering and taking the fun out of printing. The US should just outlaw the casual carrying of guns of individuals in public. That's not a violation of the second amendment.