With a 3D printer, any moron can download a design, and hit the big print button.
Yes, and any moron can blow off his hand the first time he goes to use it. 3D printers are not that easy to use. There are many variables that can affect the quality of the print. Even small variations in room temperature can make a difference in the quality of the print. When you're printing 3D trinkets or a case for a Raspberry Pi, this probably doesn't matter too much. But when you're printing something like a firearm that needs to withstand huge forces, it starts to become very important.
"Protozoa are small, and bacteria are small, but viruses are smaller than the both put together."