3D-printing - the controlled deposition of tiny blobs of plastic which can be built up to form 3D-objects - continues to grow at a nice clip. This is not only as because of falling prices for the printers, but also because of the creativity that people are showing in what they can and do make. I've talked in the past of an extreme example - medical organs - but that is still a ways off. In the mean time, we'll have to be happy with jewelry, artwork, and other common items.
But now there is news that someone has attempted to make an all-plastic gun with a 3-D printer. In this case, they didn't succeed as they were leasing the printer and as soon as the leasing company found out about it, they immediately took back their printer and ended the lease.
The concerns here are rather obvious: that someone could make and then own a gun without any permits and background checks, meaning that felons could easily acquire them. Such a gun could also not be detected by a metal detector (although the ammunition would), meaning that the gun could be brought through security in airports, courthouses and other building with security concerns.
And while these are legitimate concerns, a plastic gun is much less of a concern than a metal one. A gun made of plastic such as this would obviously only be good for one shot, and I would question if that would even work very well. Unless the gun is heavily reinforced in the back of the barrel, I would think there is a good chance that some part of it could come flying back at the shooter.