A few contradictions:
1. Does Uchiha have white blood? See:
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2. Also in the page
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tobi says he is an uchiha, but later on he tells Itachi that he is Madara Uchiha and Itachi died knowing Tobi is Madara (Which he is not) See:
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....... So all of this may be Tobi's 'I m Madara Uchiha' bluff. Also why would any Uchiha other then Madara will try to get 'revenge' on his own clan?
3. If Tobi is Madara explain how Madara was brought back as a Edo tensei? Edo tensei brings back a departed soul from the afterlife and binds it to a vessel. So if Madara's soul has departed the mortal world how can Tobi be Madara? Unless Madara had two souls or split his into half (which is absurd).
4. Tobi might have learnt the secret about Uchiha Sanctuary from Madara when he was alive. As it is clear that Madara and Tobi is related. (Moons Eye Plan and where did Tobi got or knew about Rinnegan, also Tobi has Hashi cells)
5. Tobi is yet to reveal his ability to switch from Rinnie to Sharingan or even disactivate his Sharingan.
So none can be sure WHAT Tobi is, much less WHO ...... untill Kishi reveals.