I won't argue that point with you.
However, we do know that we are all descendants from Adam. And that one thing is important to note.
Secondly:
Romans 5:19 For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous.
--It is quite apparent from Scripture that because of Adam's sin all were made sinners. We are born sinners because of Adam's sin. This is what Winman denies.
"By one man's disobedience many (all) were made sinners."
How?
It is passed down from one generation to the next, from one person (the male) to the next. It is not hard to figure this out. And the depravity of man or the sin nature of man has been a fundamental of the faith since the days of the apostles.
Your argument fails because you do not treat each side of the verse equally. You impute Adam's sin to all men unconditionally, but you impute Jesus's righteousness conditionally. That violates Paul's form of argument.
The only "equal" application is that Adam's sin is imputed conditionally to all men who sin as Adam did, and likewise, Jesus's righteousness is imputed to all those that believe on him as Jesus trusted his Father to raise him from the dead.
The only other alternative is that both Adam's sin and Jesus's righteousness are imputed to all men unconditionally which would lead to Universalism. And it is in fact, this scripture that Universalists use as their major proof text.
No, Adam and Jesus were legal precedents. They were the first, and those who followed in their steps were treated the same. Those who sinned were judged or made "sinners" and sentenced to death, those who believed were judged or imputed "righteous" and given life.