Unless he's in the Avatar State, an Avatar is not a native to the other modes of thinking outside his own element. He is aware of them, and can purposefully invoke them once he's been trained, but they are not ingrained and reflexive. The Avatar State is a (hopefully) friendly (to you) AI, drawing upon the history and knowledge and personal ethical injunctions and methodologies of all past Avatars. And it renders its verdicts with terrifying efficiency and callousness without explanation to those watching.