Let’s make an obvious scenario to find out. There is an abusive man beating a woman. If there were such a thing as the right to kill, then there would be no murder, and the man has just as much legal authority to kill the woman he is beating as the woman does to kill him. I’m this scenario, with a right to kill, both parties, the abuser and the abused, are just as justified if one kills the other.

In the case of a right to self defense, the man has no legal authority, or excuse to kill the woman he is beating. He would be found guilty of murder and thrown in prison. If the woman who was being beaten pulls out a gun and shoots the man, she would be found within her right to self defense because the man was a threat to her right to life, and his actions of beating her meant he forfeited that right. If he gets shot and lives or dies, it would be the same for the woman, because she was justified in defending her life and using force. She might be charged because the judicial system would examine the scenario and make sure her story was accurate and true, and then be released and free to live her life even though she killed someone.

That is the difference between the right self defense and killing someone, and having a right to kill.