IF Bahais believe that a human being is an incarnation of God, including Ali ibn Taleb, then that is like Hinduism that believes that Krishna was an incarnation of Vishnu. Same thing. But in addition to that, Islam is based on the said revelation of the Quran to Muhammad, and yet certain sects from Lebanon to Persia began to venerate Ali, who is not even mentioned in the Quran, that he is even greater than Muhammad himself. The Shi'a have a strong dogma of the "Imam" who existed since Adam. This is a different religion that probably pre-existed Abbasid Islam in the monotheistic friendly Arab and Persian environment. Ali was grafted onto Islam but was most clearly venerated under the earlier sect of Imamism.