The problem is there is a lot of garbage about it. Ghost guns are a real issue, but ghost guns are not 3D printed guns.
3D printed is a very niche case. They're only good for one shot ever, they are not reliable even for that. And they're bulky. The one thing they do is make it much harder for a metal detector to find them.
Ghost guns made by CNC milling equipment are nearly identical to what you would buy from the manufacturer, except they do not have a serial number and you won't have the background check for a firearms purchase.
But politicians are reacting to the ghost guns by going after the printed guns.