If we lived in a perfect world we wouldn't be having this discussion. That said, I have another spin on the over penetration thing. We know for a fact that drive buys kill people in their homes all the time. Now assuming most of those shots did not enter the home through an open window, I would have to think they went through exterior walls before hitting someone on the inside.
What I do not know is how many unintended people are struck from bullets fired in a home defense situation, through walls or due to over penetration after hitting the bad guy.
What I'm saying is, every time the home defense caliber discussion comes up, people always bring over penetration into the discussion. It seems logical that you would worry about it but is there really an issue here? I mean how many times has it happened? I can't find any stats at all.