You have always been able to do effectively the same thing for less money and with more reliability using some pipe at a hardware store. However, when someone adds the phrase "3D printing" it becomes a huge issue that people want to regulate. It's incredibly frustrating
It reminds me of a story from a friend about how strange some laws about gun registration are in the US. He was telling me of one model of gun which became restricted, but existing instances were grandfathered in. To get around this, before the ban went in place companies manufactured "unmachined lower recievers" which were literally just hunks of aluminum or steel with serial numbers on them. However, because they are registered firearms those specific chunks of metal are heavily regulated and can't be taken on planes without being locked up for instance.
The government should not be able to forbid a person form effectively defending his or herself ; it's a natural right which can't be taken away by any government. 3D printed guns gives you back that right if your state has taken it away i.e. China. They are hard to detect so this is another plus ion the same vein as the first.
This is the point of the project as I understand it, as per the project's creator.
