I think you're splitting hairs that don't need to be split. I'm not saying everyone's idiot cousin Tito who took metal shop for one semester before he dropped out of high school and now works at Jiffy Lube would be able to knock out a sear assembly in an hour. But for someone with machine tools knowledge (not that hard to get, or self-train if you had the time and patience) I think you'd agree that making your own firearms parts involves no true challenges from an engineering, materials science, or design standpoints. The technology of firearms is pretty mature and well documented, it's not like folks are trying to build a stealth fighter or nuclear submarine propulsion system; a firearm is a reasonably simple system of mechanical parts. And as others have pointed out, the value proposition of making your own firearm parts is almost certainly only going to appeal to a hobbyist and not someone looking to engage in nefarious activities. Just like the dude in this video is likely perfectly capable of building his own firearm, he's almost certainly going to just buy one at the local FFL instead just like most people would just buy a $5 digital alarm clock from Amazon rather than spend 1k hours building a bespoke clock.