In opposition to Augustinian Christianity's doctrine of 'original sin' (phrased as such by Thoms Aquinas "originale peccatum") modern orthodox Sunni Islam, in all four of its madhaahib, so far as I know, holds that 'fiTrat al-insaan' or the nature of man is basically good, and people are only drawn away from this "innate Islam" of their birth by their parents, their friends, their cultural, and their own perverse desire to rebel against Allah subhaan wa taala. And yet Islam also holds that everyone who has ever been born, and an honest reading of the Quran from the Islamic perspective-- that it was voiced by Muhammad in relation to discussions that he had with other people during his life (a ludicrous view, but not the topic of this post)-- will include Muhammad in this, must supplicate Allah for forgiveness, and must do good deeds and acts of faith to win His favor and thus in doing save themselves from the fate of the kufaar, unbearable torture in jahannam forever and ever.
So whence, then, fiTrat al-insaan? Whence know we of this innate Islam? I was listening to the Christopher Hitchens video below (I have always been fascinated with scholarly criticism of the (fake) historical narratives of Abrahamic religions, but as of late am more interested in philosophical criticisms of theism in general, Islam and Christianity in particular) and his criticism of religion, that it posits a humanity "born sick and commanded to be well", seemed at first glance to be inapplicable to Islam with its doctrine of the Nature of Man.
Yet I thought further, and realized that this is not true. Saying that we're all born Muslims and then all, without exception (or with 1 exception, the Prophet Salla Allah aleyhu wasallam, even though the speaker in the Quran frequently invokes Allah for forgiveness of his personal sins), err and become in need of the salvation economy of Islam, Salaa, zakaa, Saum, Haj, and shahaada. What is the difference here? What is the point of this doctrine? In truth, for a religion like Christianity or Islam, in the end the actual 'in practice' doctrine is and will always be original sin. If people can be good without God, then people will have no need for religion. Religions focused on sin like Talmudic Judaism, Catholic Christianity, and Sunni Islam need people to feel sick and in need of healing to justify their (the religion's--id est the religious scholars, priests, rabbis, imams, and religious social/political demagogues') existence.
fiTrat al-insaan according to Islam, if you look at what the religion really instill in its followers, in damnable, wretched, and in need of salvation. And vis-a-vis Christianity, I would say that this 'de facto' doctrine is even more destructive, since unlike the saving death of Jesus the Muslim believer has no rock upon which to place his faith in jannah, no way besides martyrdom to ensure that he is not one of the "khaasiruun" or "losers" in the next life, as the Quran so elegantly puts it.
Sick and commanded to be well indeed, Islam makes its followers sick that they might beg for a medicine which only does them more harm.
https://www.youtube.com/watch?v=-pmArHBW9ns 
Topic: The Hypocrisy and Nonsense of the Islamic Doctrine of "fiTrat al-insan"