Have these guns been used in crimes in any significant way? AR's are almost never used in gun crimes, and when they are I bet they're always or very nearly always serialized (or the serial manually removed... a file isn't a hard tool to get). This is why pro-2A'ers get so annoyed, you anti-2A'ers want to push so hard against anything gun you forget to look if these pushes do anything to help the situation or if they just harm the rights of those of us whom cherish ALL of the constitution.
Gawd. You quoted my question, didn't address it at all & then obfuscate furiously. Both 1911 & Glock 80% lowers are readily available as well as is the simple tooling to finish them. Mere possession of a firearm having the serial # filed off makes a person subject to arrest. Not so with ghost guns. They're a big plus for any gun thief, bet on that.
What's the appeal of an untraceable firearm for a lawful gun owner? What makes that a desirable feature?