It was not the mark of a fool to welcome someone under a banner of peace. Think of it, Noct: if he refused them entrance, when all believed that there would be talk of peace, what would have happened? Insomnia would have been seen as the ones to break the treaty. By welcoming them, your father exposed the empire as treacherous and dishonorable.

Furthermore, your father's actions allowed for people to escape the city safely. He died bravely in battle protecting his people.

[he falls quiet so Noct can process this. He knows that explaining the strategy of it won't ease the pain of Noct's loss, but he's hoping Noct can at least make more sense of why the king did what he did]