That is the anomaly: Why is the Tablet so instructive to activate Mugen Tsukuyomi? I don't think it stretches credulity that Kaguya's essence lingered in the world even when the Gedo Mazo was sealed in the Moon, and that she secretly influenced Madara's fall into darkness (remember the "special chakra" in Uchiha's brains that activates the Sharingan when they fall into despair, that is the Juubi's Chakra) or probably even more, corrupted the message of the Tablet.
Anyways, like most antagonists in this Manga, Madara has been setup for redemption, and what better plot vehicle for him to repent other than to be disillusioned: That he, the great manipulator, is himself being manipulated, and it's a common trope in literature that ancient evil entities are never contented to take the backseat and let another antagonist take the lead, she will overtake him eventually.