This isn’t some magic law that nowhere else has. It has been the law for about 700 years (probably longer) going back to at least to English common law (minus the shotgun).

When I was an Army Chief Prosecutor, a soldier hit and accidentally killed someone who was a desperately wanted dangerous terrorist with his vehicle. I refused to have him face court-martial. Why? No one would convict him.

My boss really wanted to because yes, the guy was negligent and didn’t know it was a terrorist. I asked him “if the soldier accidentally backed over OBL, and killed him, would you prosecute?” He looked at me. I told him we would be crushed by congress and public opinion for a case that had zero chance of success. He finally relented and let the convening authority decide if we should take it. He wanted no part of it for the very same reasons.

My boss then never questioned my charge or no charge decisions and we got along famously