So this question has kind of been nagging on my mind the past few days.
Do you have to believe in the literal interpretation of Genesis in order to believe in original sin?
I take the words at face value... are there symbolic or possibly symbolic meanings - for instance - in Genesis? Yes.
For instance, in the creation of the world, there is some unusual discussion of the creation of a "lesser light" and "greater light"... and "birds of the air and fish of the sea", and so on... which allude to matters of much greater meaning then what they appear of as first -- just as the "snake" in the Garden of Eden was later positively identified as Satan, who is also identified as "the Destroyer", also called the "Destroying Angel".
What is "original sin", some argue that because Adam sinned, therefore everyone "has sin" from that first sin.
Romans 5
12Therefore, just as sin entered the world through one man, and death through sin, and in this way death came to all men, because all sinned 13for before the law was given, sin was in the world. But sin is not taken into account when there is no law. 14Nevertheless, death reigned from the time of Adam to the time of Moses, even over those who did not sin by breaking a command, as did Adam, who was a pattern of the one to come.
...
18Consequently, just as the result of one trespass was condemnation for all men, so also the result of one act of righteousness was justification that brings life for all men. 19For just as through the disobedience of the one man the many were made sinners, so also through the obedience of the one man the many will be made righteous.
1 Corinthians 15:22 (New International Version)
22For as in Adam all die, so in Christ all will be made alive.
"Sin is not taken into account where there is no Law."
Why did Adam die? Was Adam not sinful before he ate of the tree? Put it this way: "only God is good", and as Adam was not God, he could not have been good to begin with.
But as Adam was oblivious to his own sinful state, not even knowing he was naked... he was not culpable for anything and therefore not sentenced to die... until he ate of the Tree of Knowledge of Good and Evil... and then he became culpable for his sinful state and culpable for his sins, which lead to death.
And since then we have all been culpable for our sins.
There may not have been commands which were broken, but as Paul explains elsewhere in Romans, even those "without the Law" show by their own actions that "the Law is written on their hearts". And it has been pointed out by some that in the Law is "all knowledge of Good and Evil". Put one way: the Law basically made conscious what was in the heart of man.
And the fulfillment of the Law can be summed up by "love the Lord your God with all of your heart and strength" and "love your neighbor as yourself". But man does not have such love in his heart -- in fact, how can he possibly love God whom he does not see and so can not comprehend? He can love his children, his wife, his family, his kin and kind... but love for strangers, they do not do.
God, conversely is love.
Man had life, but not eternal life: man had a semblance of the love that is God, but not the overabundant love that is found in eternal life.
Man was created in the Image of God, but is not God.
Was man effectively sinful before Adam ate of the Tree of Knowledge? In one sense, "no", because faith is what brings about righteousness and he would have had complete and yet simple trust in God. So he would not have sinned.
But he still was not God and only God is good.
Why was creation subjected to such "futility"? "So that many Children of God might be born". So that man might become spiritual man, like God, who is Spirit.