I would point out, however, that your viewpoint appears to be U.S.-centric. In the U.S., you can 3D print all the "easy" parts (pistol frame, rifle stock--parts that could be whittled out of a larger piece of plastic, molded from epoxy, or similar), but you can buy all of the "hard" parts without restriction since they're not legally the firearm (barrel, chamber parts, etc.). I bet that varies a lot country-by-country.
And another idea I have: a lot of the "vastly easier" manufacturing you're describing is actually a product of the interconnection the internet has wrought, rather than 3D printers specifically. If I imagine a world where we didn't invent 3D printers, but we do have the internet, I bet we could've captured most of the manufacturing-ease gains other ways. For instance, just produce molds and then mold parts out of fiber-reinforced plastic. It makes iterating on designs harder, but we have a lot of people + the internet. So the process would be slower, but we would get there. Neat, huh?!