Discussions with believers about this are always circular:
Me: "Why am I being punished for Adam's sin?"
Xian: "Your not, your being punished for your own sins."
Me: "How do you know I've sinned?"
Xian: "Everybody sins."
Me: "How do you know that?"
Xian: "Because it's in our nature."
Me: "Why do we have such a stupid nature?"
Xian: "We inherited sinful nature from Adam."
Me: "So why am I being punished for Adam's sin?"
Xian: "Your not, your being punished for your own sins."
And so on... Avoiding the question by rearranging it.
But either way you look at it, we either inherited sin or 'sinful nature' from Adam. And either way, it's punishment for someone else's error.
Why aren't humans born perfect, until they sin? That is the question. If they are not born perfect, then it's punishment for someone elses sin, AKA injustice.
By the way:
The Watchtower equates Adam's sin as the theft of a perfect life. So according to Exodus 22:1 Divine justice states that Jesus is going to have to come here and die three or four more times...
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