Even if someone threatens you, you shouldn’t kill anyone. Why is your life worth more than the life you take? It doesn’t make sense. I believe people have a 100% right to live unscathed in the world as long as they don’t hurt others. So if someone does harm to a person he should be liable for that.
Everyone should answer for their own actions. The person who threatened should answer for threatening, the person who assaulted should answer for assaulting. However I believe most people would forgive the person who harmed them because he was threatened. Those who won’t forgive have different set of values, and it is their right. I believe no one has the RIGHT to hurt another person no matter the circumstances.