I think you're dodging the point. I already said I was in favor of stronger licensing, insurance, and training requirements in a failed attempt to avoid that rebuttal. If somebody steals something from me in the middle of the night while I'm asleep, something I was legally allowed to have, and they use it to commit a crime before I notice it's gone, I should not be punished unless I was negligent in where I left it.
I also don't understand the design argument. Cars are used to kill people efficiently all the time. Doesn't matter if they were designed for it, they do it. If you want to go down that route, I would say the guns I own were designed to put holes in paper from a distance, because that's all they've ever been used for. My guns, like my car, have a zero percent fatality rate. There are a lot of people in the world who can't say that about cars they've owned. See how silly the argument gets?