The doctrine of original sin states that since Adam represented all mankind as its Federal Head, his sin in the Garden of Eden resulted in every human being after him to have a sinful nature and be guilty of his sin.
This means that even from conception, every human being is guilty of sin before God because of Adam's sin.
Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned... For as by the one man's disobedience the many were made sinners, so by the one man's obedience the many will be made righteous.
Here, Paul teaches that because of Adam's sin in the Garden of Eden, "sin came into the world" and "the many were made sinners." So, even apart from any personal sin, every person is guilty of Adam's sin.
Some argue that it was not fair for God to make Adam our Federal Head and representative, and that He should only judge humans according to their personal sin. However, the doctrine of original sin is fair because for least two reasons:
Below are several more Bible verses that show humans are guilty from the very beginning.
Behold, I was brought forth in iniquity, and in sin did my mother conceive me.
The wicked are estranged from the womb; they go astray from birth, speaking lies.
That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.
And when the Lord smelled the pleasing aroma, the Lord said in his heart, “I will never again curse the ground because of man, for the intention of man's heart is evil from his youth. Neither will I ever again strike down every living creature as I have done.
Folly is bound up in the heart of a child, but the rod of discipline drives it far from him.
Scripture is clear that humans are born guilty of sin because of Adam's sin in the Garden of Eden. Adam was our Federal Head, and therefore represented the entire human race when he sinned.
The doctrine of original sin is not unfair, but is rather a part of God's perfect plan to glorify Himself and grant inexpressible joy to His people, who get to experience the happiness of God's free grace to undeserving sinners.