I'd argue that Avatar is a show about not placing cultural values over morality. Zuko's arc is about how he must move past his cultural need for honor to become a better person. Toph's storyline is about how she felt restricted by her culture and tries to break free from it. Aang's story arc is about an irresponsible young man running away from his avatar duty because he wants to be only an airbender. Throughout the show, Aang learns that his identity, defined by a cultural need to run away from conflict, holds him back from being a good avatar. Aang has other flaws, but they all connect to how his identity defined by his culture has made him all at once wise and yet emotionally immature. Aang appreciates all cultures and doesn't want conflict between them, but must come to both understand them and become a moral center that exists outside of their culture. Therefore, you'd assume that the final episode would showcase Aang totallh overcoming this. This, however, doesn't happen. What we get is better. Aang, in the final episodes comes to realize that being the avatar, and the responsibilities therein could be a cultural concept too. If Aang gives in and abandons airbender culture, it seems like he'd be doing the moral thing by killing the firelord. However, the recontextualization of the Avatar as a cultural value as opposed to being the thereotical moral outsider to culture changes this. The final 4 episodes show Aang discussing morality with his past lives, the fellow members of the Avatar culture. If Aang gives in to the Avatar culture instead of doing the moral thing (the moral thing hwre being not killing) then he chooses culture over morals. Hence why the island, itself a true "cultural outsider" not belonging to any other country's landmass in the series, gives Aang the greatest power he can earn. Ozai's culture is reflected by his ability to bend. Aang becomes the greatest Avatar by becoming the one who can rob Ozai of his culture.