Why a 3D printed gun?
It doesn't shoot straight, or far, and will probably blow up in the shooter's face. It's more of a danger to the shooter and anyone nearby. For crying out loud, if you feel you need a gun for protection, buy a good one and not one that's some guy's idea of a proper firearm. Then take the time and spend some money and learn how to properly and safely use it as well as properly store it.
Disclaimer: I don't own a gun (but have in the past) and for the foreseeable future, won't own one either. But I understand some folks feel the need for self protection.