People like you, who are still on the concept of good and evil. There is no such thing in the world of Destiny. Think of it as the wilds of the animal kingdom. The fittest of the animals live while the weak are crushed or eaten. So is the world of destiny, but in a much larger scale. Light and darkness do not equal good or evil. Just two halves of the same spectrum. Our traveler is not evil, just as The Black Heart isn't evil. It's our god. It wants to be the only god, just as the other gods do. It's not about who is right, it's about who is left.