I like this idea in theory, but in practice if I see Dick Cheney coming at me with a butcher's knife I'm getting the hell out of there.
He prefers to become your friend over many years, have great experiences together, then shoot you in the face and make you apologize for your role in the incident.
While it's primarily the responsibility of an upland bird hunter (anyone shooting, of course, but in this sort of hunting you move around a lot and flush out birds unexpectedly) to keep track of everyone and not shoot when any of them are down range, everyone in the hunting party also has a responsibility to follow previously agreed upon protocols to make this easier and less error prone. The guy who got shot screwed that up big time.
Of course A)as VP Cheney's life was already a media circus B) Cheney shot the dude in his face and assumed-risk-or-no Cheney bears the responsibility for that.
In ~70 years of it, one of my father's favorite pastimes, he got shot exactly once, although there was no excuse for it like there was in the Chaney accident. Then again, he was both careful in picking his hunting partners and only hunted with some of them once after they demonstrated they didn't have their act together.
As long as you wear glasses and there's some distance, serious injury is unlikely, as happened with him. A tough shirt is also recommenced, that stopped penetration of the shot that hit his chest.
I live in Texas so it would permit certain actions on my behalf.
edit: The difference is that some states have a requirement that the defending party retreat. Got it. For my part, I imagine I'd always retreat if given the chance and if it's reasonable (ie, I'm not going to retreat and leave my family in harm's way, etc). Of course, I can't fault anyone for making a different choice; who knows how one might act in such a situation.
In various parts of e.g. Europe, though, that would get you a prison sentence, very notably the U.K., since you would be using more force than the aggressor. The US principle is that once the threshold of lethal force is reached, other forms of lethal force in response are legitimate.
Of course this is probably untested in court as no one here carries a gun.
It can most certainly come up in home invasions, another article by the BBC mentioned about 11 cases in the recent past.