I would submit that by protecting others we are always protecting ourselves. If someone has by their actions placed themselves in the position that they can be legally shot, I'd say they've demonstrated through their actions that they will continue to be a threat in the future.
Really? Like the drunk who stumbles into the wrong house? Just blast him to protect the public from inchoate future harm?
Is every person who commits a felony equally culpable? How about an "armed" felony? Blanket "deserve to die" culpability? No matter what?
Your view brings back the Bloody Assizes, albiet now its private....
Here: Isn't a retreat, even in one's home, a personal means to determine the true culpability of the criminal actor? if one doesnt retreat, and merely just fires away, doesnt one have a measure of moral culpability in a death? Is it all a question of degree, or a simple act/react? if the latter, why should even the law have nuances?