But I think self-defense is an ethical form of violence. Although it should always be proportional and explainable afterwards. And killing someone is only justifiable when there's no other way out in that moment, when it really is the last thing you can do when there is a direct lethal threat. In war situations things can become more complicated, but even then people in combat should try to avoid casualties to the max. (and also in self-defense of course).
2/2