The Sin of Adam

1. God forgives all sins except the sin of blasphemy that is ascribing divinity to other things beside Him.
An example of blasphemy is elevating Jesus to the status of god incarnation.
2. God loves His creatures and is compassionate in all His dealings. It is unthinkable that He refuses Adam's plea for forgiveness.
3. God is the fountain of justice. He would not make descendants of Adam suffer for his sin. Making them suffer, amounts to taking revenge. God does not do that kind of thing.
4. The sin of Adam is nothing compared to the sin of Israelites who worshiped the golden calf in Exodus. Yet, the Quran says, God blots out the sin of those Israelites. Surely He would do the same with the sin of Adam which was comparatively much smaller
5. God said in the Quran that He has accepted the repentance of Adam
6. Even the Bible states that one is responsible for one's sin only and is not responsible for the sin of others

Where does the doctrine of original sin begin?