Every one on the internet assume that their shots will kill the 'perp' dead and that will prevent pay back or law suites. What if he doesn't die. Going to shoot him in the head on the ground and defend that with the Castle doctrine? That will be a fine test case.
Well, maybe he is a gang member and many come to your house. Maybe his family will sue you as the forensics show that he wasn't a threat as he was just a drunk who wandered in.
And horrors, all you steely eyed dealers of death think you and your family will come out of a killing happy as clams.
Lots of research show that you may be psychologically and socially messed up. That's why lots of folks teach a challenge if possible.