Don't make such blanket statements uninformed. These laws vary widely from state to state. In most cases, your life does NOT have to be a risk to defend yourself with deadly force.
That's not true. In every state one of the required elements for valid self-defense is that you have a reasonable fear of death or great bodily harm. You might defend another person, but that requirement still exists applied to the other person. There are jurisdictions where you can use force in other situations, but those aren't self-defense.