That's right, illegal would be illegal. A 3D printer is just another tool. Perhaps it's an issue because it's easier to make something? Download, slice, print. Perhaps it's the convenience? Or requires a lower skill level?
Keeping an optimistic view, 3D printed parts are something else that forces the real issues on the table, and it's not gun control. Among many things, it's a social problem. Yet the (supposedly) well educated leaders of our great country can't make common sense decisions. Any laws or regulations that may get passed will demonstrate their ignorance or intelligence.