The saving grace, such as it is, is that these firearms are single-shot, and the rounds themselves are still metal and explosive-residue-detectable. While 3D printing has changed manufacturing methods, it's not like the method of deposition changes the strength of the material that much, so it's improbable that these plastic firearms will ever be able to withstand more than one or two shots.

It strikes me as likely that a 3D-printed gun will not be the most effective way to accomplish almost any kind of harm for almost any kind of perpetrator, no matter how situated. And that gives me a little comfort, even if I wish my countrymen were less fascinated with weapons.