Consider Daniel Shaver, he was crawling on the floor with no weapon, but the police suspected he had a gun and was about to shoot them, so they shot him. The courts found the police not guilty.
The article is about government property (a courthouse) not commercial property.
For example: https://www.sltrib.com/news/2018/06/20/security-guard-shoots... (slightly more elaborate, but still a man shot in the back and and killed when peacefully leaving an area)
Also defending another person against a threat to life is a basis for the use of legal force everywhere - that’s pretty uncontroversial I think.
The 'castle doctrine' you refer to is a perversion peculiar to some US states, but it still has to be your home and you still have to have a reasonable belief your life is threatened. Strangely, although you can use lethal force on an intruder/trespasser, if you shoot a police officer about to conduct a lawful no-knock raid, I think you could get convicted.
https://www.texasmonthly.com/news/a-no-knock-raid-in-houston...
Only a few states have castle doctrine laws in effect, and there are restrictions on when they apply.
When all you have is a gun, everything is a nail that can be shot at.
Ref:
https://americangunfacts.com/pdf/www-telegraph-co-uk.pdf
"2034[1] vs 466 Violent Crimes UK vs US per 100k people"
[1] The July 2009 Telegraph article says "over 2000"
Just last week there was a home invasion robbery and the mans guard dog was shot and killed in my current city.
Slightly more than one in a billion chance.
Guns can’t be taken out of citizens’ hands. Teach responsible use and double down.