what does that have to do with anything ?

It wasn't a sarcastic comment. school shootings in the us are really common, so eventualy someone is going to do it with a printed gun.
The shuty would actually be a great candidate.
At some point, possibly, maybe, people might try and limit childrens access to guns in the states (i'm not holding my breath). At which point your 3d printed option will definitely come into play.

use a carbon fibre barrel if you want to get through a scanner. Of course you'll also need to make your own non-metallic ammunition.
Getting a firearm through a metal detector is definitely not what anyone should be worried about.
There is always a way round that.

Single use, illegal weapons that can be disposed of in a trashcan fire and are completely untraceable, would be my issue if I were a leo.