Just be thankful that you do not live in the United Kingdom.

Legally: You can use deadly force if you are faced with a situation in which a "reasonable" person would conclude that their life or the life of others is in jeopardy

The practice: You will be charged with murder. You will be put on trial. The jury will be told that there are no circumstances under which killing them could possibly be justified.

Despite the fact that you enjoy the presumption of innocence, you are going to have to prove that you had no other choice. You are dealing with a jury that has no understanding of the situation. How have been repeatedly indoctrinated with the idea that violence IS NEVER EVER justified.

Which is nonsense.
I don't do dumb & helpless.