Aeneas' killing of Turnus was right and justified. He was in a battle to the death. Only a fool would have spared his enemy in a fight like that. Some argue that by sparing Turnus, he would have gained a valuable ally. But the reality is that Turnus had broken his word before when he promised to fight Aneas to the death the first time. What would stop him from lying again? He could have easily gathered more troops and tried to wipe out the Trojans. When Aeneas considers sparing Turnus, he is being humane. But he has forgotten that Turnus is his enemy who would have killed him in a second if their positions were switched. Thus, when he sees the belt of Pallas and kills Turnus in rage, it is a justified rage. Aeneas remembers how brutely and mercilessly Turnus killed his friend, Pallas. This causes him to do what he was supposed to do, kill Turnus. He was justified in doing so.