The article focuses on a particular gun, the AR15. After much wrangling, settled law dictates that the "lower receiver" _is_ the gun; all the other parts are incidental. Sure, the lower receiver alone is little more than a big paperweight, but it's the unchanging core to which all other variable components are attached to form something functional. And no, you can't just "whittle it from wood" etc., it's a pretty serious chunk of milled steel (there exists a "plastic" version, but that ain't generic plastic).

Yes, some jurisdictions aside you can make one AR15 lower receiver on your own without any paperwork, fees, checks, or permission. Understanding is that nobody going thru that much effort is going to waste it by doing something stupid (if there's criminal intent there are many far easier ways to acquire one).

The issue here is: where's the line on making one? You can make one yourself legally, but if you hire someone else to knowingly make it they'll need an expensive big-hassle manufacturer's license. The key is "knowingly", as up until recently it was pretty obvious to the machinist what he was being asked to do. Now, with "printing", you just upload the pattern for what is otherwise just another odd-shaped chunk of metal, a computer & machine crank one out, and the result gets sent back to you with a minimum of comprehension by any humans involved - are _you_ "making" it? or is the printing house "making" it and, in effect, selling it to you? The legal line has been blurred.