It could be said to be an ingenious plan. By the journey's end, the Successors will have seen the worst humanity could do. But they will also uncover its extraordinary beauty and brilliance. While they might have started naïve, the legacies would have granted them immense wisdom.
White knights were disparaged because they were far too ignorant. But the same can be said about anarchists who knew nothing but darkness. If a man grew up knowing nothing but hate, then of course he would wish for the end of the world.
But if he knew love? Then it became incredibly difficult. Ending the world eliminated the trash, that was true. But it also destroys the chance of kind-hearted people being born. Many anime and manga struggle with this same existential point.
Man was said to be like God not for his form or his intellect. It was because he had the power of choice. Within every human resided not only the potential to be the vilest demon but also the noblest hero.