The whole idea of moral greyness is so stupid, vapid and immature. How can you classify humans as 'grey' (ie contain both good and bad) without a definition of what good and bad actually are.
Black and white morality is important to understand. Without pure good and pure evil, you have no standard of value to understand grey morality. If you want to be the best person you can be, you have to have objectively Good goals and values to shoot towards. Grey is filthy and doesn't inspire you to be a better person in an already grey world. A story of good vs evil being "intended for children" means it is inherently good for adults as well. We want the best for a children, it's why we create media for them that helps nurture their growing heart and soul and mind. A man or woman inspired by a simple story of good and evil is as much a treasure as children learning the dichotomy of good and evil through those same stories. It's why we as peoples have always been drawn towards and enjoy such fables. It helps us, young and old, to remember the correct path for happiness and healthiness. Morally grey stories are simply for entertainment purposes only, because we already live in such a reality. They can also be cautionary tales, but they should never be consumed and heeded in such ways that you would apply the morality to your own life.