Why does Tobi put up a goofball facade initially? 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?
Tobi acted like a goofball to hide his true nature. Pein was the leader of Akatsuki, but


   Tobi was the one pulling the strings behind everything so he had to mask his true identity and seem unworthy of investigation.


Tobi made himself look weak and useless, which is perfect for his disguise.