Why is it that the Muslims do not accept the doctrine of original sin?
The reason Muslims do not accept this doctrine is that the word of God, the Qur'an, does not agree with it. The Qur'an teaches that God is ever willing to forgive anyone who turns to him in sincere repentance. We find in the Qur'an that God taught Adam and Eve how to seek His forgiveness. When they did as God taught them, God forgave them (see Qur'an 20:122).
Adam and Eve were created with the potential to do either good or evil. They had a free choice either to obey God or disobey Him. They did not realize how deceptive the devil was, and so prompted by him, they made the wrong choice. Will God remain forever angry with them over that one mistake? No! Instead, God taught them how to repair their relationship with Him by praying for forgiveness. Muslims still often recite the same prayer, as follows:
Our Lord, we have wronged our souls. If you do not forgive us and have mercy on us, then surely we are lost (Qur'an 7:23).
What we obtain from that incident is not original sin, but original forgiveness, and an original lesson on how to seek that forgiveness. God set the precedent that He will forgive those who turn to Him in sincere repentance. We will all find ourselves in a similar situation as Adam and Eve. The prophet, on whom be peace, said that every child of Adam is a sinner, and the best of them are those who turn back to God in sincere repentance.
This shows that God does not demand absolute perfection from us humans. That would be an impossible demand, since God alone is absolutely perfect. To err is human. God wants us to know that he will accept us as we are, shortcomings and all, as long as we are trying our best to obey Him. Even in our human situations, it is well understood that absolute perfection is not to be demanded from anyone. Suppose teachers were to demand that all students must score 100% on all their tests, and that if they make even one mistake they will not pass. No one of sound mind will demand this, for it is clearly beyond human capacity. Similarly, God does not demand from people what is beyond their capacity (see Qur'an 2:226).
Some will say that Adam was created perfect and that when he sinned he ruined that perfection. This suggestion makes no sense. If perfection meant that Adam had no ability to choose between good and evil, then how did he exercise that choice which he supposedly did not have? And if he had the ability to choose, as Muslims believe, then why would God remain forever angry with him for his first mistake? Humankind was then in its infancy. We needed someone to pick us up when we fall, not someone to bulldoze us with a tremendous burden of sin and guilt.
Some will say that God could not forgive Adam even if He wanted to do so, since God is Just and He must exact justice. This is as if to say that justice is contrary to mercy, and that God is so fenced in by His own law that He has no freedom to do what He wants to do. How silly! The truth is that God warns us of His punishment, but He also promises forgiveness for those who sincerely repent. If He decides to save sinners, who is there to say He cannot do what He wishes?