Righteousness is in the eye of the beholder. If in the act of defending yourself, you kill somebody, is that objectively a good righteous thing? Is that not a bloody stain on the world? Will there not be blood on your hands? Would you be happy about the fact that you killed somebody for the rest of your life? Will you always feel that it was righteous to do so? And do you think anyone in a similar situation should feel perfectly justified and freely killing anybody who they feel threatens them in self-defense to just kill and that this is the right thing to do?

I totally agree. Any good person who has to kill another person is going to question it for the rest of their lives. That's the issue. A not as good person doesn't care. It's better to live in regret than not live at all. It sucks so fucking much that anyone has to deal with it, but the world sucks. There isn't a perfect answer.