The problem is what the title implies. If a person can print a gun using plastic, it's undetectable by metal detectors. That would pose problems for airplanes, courts, government buildings etc. That's why most ceramic knife makers speckle their blades with a metal.
I understand that it seems impossible to detect the plastic but there are still the bullets to detect. Also, airlines are already one of the best if not the best protected sector. You can get into a bank with less hassle than board an airplane.
Just for fun, think about a system where all weapons can be detected.
It is still possible to use poison on the pilots, to use a LAW to take the plane down and one could even get a job at an airport to sabotage airplanes. People have for smuggling drugs for instance so why not?
What I am trying to say here is that there is no stopping the really motivated. Setting up rules or prohibiting certain items is security through obscurity in my opinion. Guns and most knifes are illegal where I live, still I know people can have access within an hour, 14y/o kids use guns to rob people... Laws don't seem to mean much to criminals.
There is no stopping loonies, there is no stopping terrorism, only reason most people think it can be done is because politicians tell you so. Still, in Iraq and other places it is proven you can't really fight it, you can only fight the things that fuel it.
To think we can get the world a bit safer by forbidding items like the OP posted is a fairy tale. But, that is my opinion.I don't expect you to share it.
On a side note, if you speckle your knife with metal, in an age where plastic can be used to make knifes too, I wonder who feels safer by that. A plastic knife won't last 50 years of course, but they only need it for a day...
False sense of security me thinks, just like adding a scent to Semtex while there are some countries known to supply all sorts of weapons to terrorists, including explosives.
For the record, I am not promoting terrorism but I think it is insane to be treated worse than a criminal just for taking an airplane to somewhere. Especially because it doesn't mean the airplane is any better off against the really motivated.
Banning guns and sorts is very much like forbidding matches to the general public because there are arsonists amongst us.
