3d printed plastic guns are real in a sense but not in any practical way. I am not sure why so many people think this is a concern. If I have a box of ammo, I can probably go into my shop and come up with a way to fire it. I doubt I would use my 3d printer in that project though. There are better ways to makeshift a weapon.
I have to know what the Detroit soccer team did to get so high on that list. Somebody here must know. Please!