I can agree with the zetsu theory, and zetsu was a creation so he kinda is a "no body" no history etc. maybe thats why Oro left akatsuki he got mad that zetsu took over. Also would explain why tobi who was pretending to be madara waited so long to attack the leaf. Every theory can be argued for and against. I think we keep spitting them out so that in the end one of us can say I TOLD YOU SO.