how am I to know where you would stop escalating the violence you initiated?
With reason, logic, and evidence? Humans are emotional beings and they make emotional mistakes. If someone screws up and lets their negative emotions get the best of them, and you'd be willing to end their life because of it, that to me seems like a moral framework so rigid as to be worse than Statism's victimless crimes or some hyper-dogmatic, fundamentalist, violent worldview. Punishment based on harm done to the victim has to be rational. When it's not, we get the State or ISIS.
Worse than stateism victimless crimes? Seriously? Say you initiate aggression and slap me when I have not done anything that constitutes aggression towards you, and I proceed to hand you an ass whooping, how do I know you won't come back with a knife or a gun?
Now I'm not saying that I would always or automatically resort to lethal force. That would only happen in cases where I felt the threat of escalation by the aggressor was a real possibility, but under THOSE CIRCUMSTANCES I maintain that I am within my rights to assure that I am not the victim of further aggressions.