Something tells me if someone broke into your home and threatened a loved one with a knife, you would not hesitate to use deadly force against them.
While I have long expressed distaste for "what-if" hypothetical games and generally refuse to engage with them, I will say that I would do everything in my power to use
non-lethal force to apprehend them and turn them over to legal authorities for fair trial
as is the right of every human being under Articles 7, 8, 10 and 11 of the
Universal Declaration of Human Rights.
Lethal force is
at best a last possible resort when there is absolutely no other option. Using a gun for lethal self-defence completely undermines this principle. It bypasses even the slightest question over whether lethal force is even necessary.
You see someone who is apparently threatening a loved one with a knife, and you have a gun that you profess to own for "self-defence", so you shoot and kill them. It matters not whether they actually intended harm. It matters not whether there is any mitigating circumstance. It matters not whether they have loved ones who might be grieved at their death. It matters not whether the knife is even real and you haven't misinterpreted the situation. You have taken the matter into your own hands and in the spur of the moment you have unilaterally decided that this person deserves to die. In a fraction of a second you have appointed yourself judge, jury, and executioner. In a fraction of a second you have issued judgement, and in a fraction of a second you have dealt out the most irrevocable of punishments.
Can you even live with yourself after doing that?
Regardless, the use of lethal force in self-defence is legal and common in the United States, in a way that is practically unheard-of in other developed countries. This utter disdain for human life and dignity that is enshrined in US law is well-known, and it applies to everybody in the country.
No wonder the place is so ◊◊◊◊◊◊ up.