... But deadly force should only be used to defend people, not stuff.
That is a common philosophy, but it is philosophy not law or even morality.
Many people believe that deadly force is justified, morally at least, to protect property.
The alternative is to allow criminals to steal anything that they can escape quickly with, and there is no way to stop them.
That may not be practical.
Besides, I put part of my soul into much of what I have. The one who steals it steals part of me.