This isn't about personal responsibility, it's about safety and security. The people who want to ban 3D printed guns (and guns in general) are the people who don't use or want to use guns and want to even the playing field for themselves by getting rid of guns altogether.
Where does the personal responsibility come in? I don't expect the people who are 3D printing guns are all doing it for personal safety and security. I imagine some of them want to print guns so they don't have legal traceable guns and want to go kill people with them and I don't want one of those people killed to be me.
Should we really wait for someone to go on a killing spree with a 3D printed gun or any gun for that matter until they "prove" they can't handle a level of personal responsibility? No, we should probably be proactive about it and limit the ways people can have access to dangerous weaponry.
Why do you find it insulting? When you're given a weapon without training or practice it SHOULD be assumed you're not going to be responsible with it. We require licenses to drive because cars are dangerous without proper instruction, as are guns and most things that we need licenses to operate.