GREAT question.
As someone who has participated in martial arts for over 20 years now, I’m alway stunned by the actions of some people who almost try to look for reasons to beat someone up. They say, “Well, if someone breaks into your house, you have to the right to kill them! Or, If they steal my car!” NO! THat’s an awful thing to say.
What I teach my students is this-You never, ever, ever try to kill a person, period. What you do is take the necessary steps to protect 1) the life of your family, 2) your life. You never kill someone in order to defend your property.
Now, I’m a pretty good show with a handgun, and I’m very skilled in certain martial arts. I am confident I could incapacitate someone without the need to kill them. Other people may not be as confident as I am.
To make it clear-if someone has a knife and is running towards a loved one, I would make the attempt to disarm them, not kill them. However, I would do what it takes to stop them from hurting my loved ones.
Only if it was a last resort (The man had opened fire with a gun in a crowded mall) would I feel it is moral to kill someone.
Hope this helps a bit.