[AngryData]

It is fearmongering. You technically can print an all-plastic firearm that works for a round or so until they explode, but only after you have already printed and tested and refined multiple times over, and best case it is still an inferior material to metal. I would put it in the same category as "Yeah you can turn a tree trunk into a cannon, tell me when not to come over when you use it." You can probably make a similarly reliable firearm out of fired clay if you put in the same effort.

Some parts in regular firearms can be printed in plastic, guns with polymer parts have existed since polymers existed, but it is only marginally simpler than machining it out of metal. After all you can buy a metal CNC machine for handful of bucks more than a 3d printer and you don't have to worry about shitty materials breaking immediately.

And there are already plenty of examples of hardware store pipe guns that if someone spent more than a day or two working on it would by far surpass anything anyone can print.