This question contains spoilers
Tobi introduced himself as Madara to Nagato and Konan. Zetsu knows his real identity. He showed his real face to Kisame. Itachi at least knows that Tobi is not a goofball (if not his real identity). Why did he have to put up a goofball facade for Sasori, Deidara, Kakuzu and Hidan? There were reasons to keep his real identity hidden, but why did he not introduce himself as Madara to the whole group?