I used to frequent the FOSSCAD IRC ages back as a teen. This started during the post-Liberator panic, there were talks about regulating 3D printers to not allow printing guns, etc. Designed a few things, never actually printed any of it myself, but some others did. Really got me into engineering before I exited the scene, led to actually pursuing an engineering career. Was surprised to see 3D printed gun videos so openly shared, it was pretty underground for ages there.
I used to run the 3D printing community on G+ at around 500k strong, (about 10k weekly active users according to Google's stats) and I ended up actually pissing off a lot of my European users because of this. My viewpoint on it, was as an engineering exercise -- it's an amazing thing. It's not advocating for guns, and guns aren't only used to kill other people. So I stood up for the guys posting about their engineering challenges, and their work making 3D printed parts for a machine with high impact loads and loads of cycling issues.
Unfortunately, it lost me some friends, like Gina Haubage and Tomas Sanladerer -- as they disagreed highly; and wanted to ban anyone posting firearms related 3D printing content.
Projectiles are a part of human nature. We've always thrown spears, rocks, etc -- firearms are just an extension of our better understanding of the world. I know of barely anything else that uses explosive charges that is as widely applicable to the general public. Roofing nail guns? But that's such a niche subject, it's not something people are really worried about trying to make with 3D printing. Believe me, if I had a better engineering challenge for 3D printing, I'd be suggesting it. But nothing quite hits like containing an explosive charge, and utilizing the energy in a way that performs work without destroying itself.
Absolutely, it's a fabulous engineering challenge, to make it work well on a hobbyist grade 3D printer with ordinary materials. Also a lesson in using the right tool for the right job (some parts are just better off milled or bought OtS)