Why do I have to be punished for Adam's sin?

Since Adam disobeyed God and now has a sinful nature, he caused every man after him to be born with a sinful nature. The term used to describe this condition is "original sin" or "inherited sin." All humans have adopted this sin nature through Adam's original act of disobedience.

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Romans 3:23 — for all have sinned and fall short of the glory of God,

Rom 5:12-19 — Therefore, just as through one man sin entered into the world, and death through sin, and so death spread to all men, because all sinned--
for until the Law sin was in the world, but sin is not imputed when there is no law.
Nevertheless death reigned from Adam until Moses, even over those who had not sinned in the likeness of the offense of Adam, who is a (Or {foreshadowing}) type of Him who was to come.
But the free gift is not like the transgression. For if by the transgression of the one the many died, much more did the grace of God and the gift by the grace of the one Man, Jesus Christ, abound to the many.
The gift is not like {that which came} through the one who sinned; for on the one hand the judgment {arose} from one {transgression} resulting in condemnation, but on the other hand the free gift {arose} from many transgressions resulting in justification.