With international affairs, isn't stopping the aggression the main priority? That is stopping the death and suffering of humans on both sides? Sure it would be good to punish the aggressors rather than the retaliators but if that doesn't stop the fighting it just means more people are dying.

Also there is a difference between the adult and the child, the adult relies on the law of the land for retaliation the child takes it upon himself when he continues the fight. That is the child is a vigilante, and he may punish disproportionately e.g. breaking a leg for a dead leg.