Historians have never knew what he meant to represent, but the fact that his work shows a conflict between good and evil is present. So there is no question Billy is the utmost good. And in my opinion I think what Melville means to say is, evil can't triump over good, and good can't triump over evil. You have to realize that Melville was anti-transcendentalist. He saw that in the universe, you can not deny the presence of evil.
Evil is always present.
Unlike transcendentalist who say everything as good, and saught human perfection. Historians have never knew what he meant to represent, but the fact that his work shows a conflict between good and evil is present. So there is no question Billy is the utmost good. And in my opinion I think what Melville means to say is, evil can't triump over good, and good can't triump over evil.