I was challenged recently that the idea of original sin and Adam's fall as our Representative Head was an unfair and antiquated idea. Nobody still believes that today, do they?
The push-back was not on universal sin, a cursory read of the Bible (or the newspaper for that matter) will settle that one. We're all sinners, no son of Adam (save one) has ever lived a sinless life. "But this idea that we are sinners because Adam sinned, that's so archaic!"
As I considered an answer, I was reminded of a similar complaint. Why did God make humans so we could sin at all?! Why not create us so that we would always choose to love and worship God? The answer is that this sort of love and worship would not be real, would not be genuine. In order for our love and worship to be real, it must be free.
So God created the first two humans with genuine moral freedom (a freedom we don't possess or fully understand). God made them this way not because he wanted humans who would sin, but because it must be so in order to have free God-worshippers.
The nature of God-worshipping freedom requires it.
And I think this may illuminate our question of the imputation (or the passing down) of sin. Just as the nature of freedom played a role in the sort of humanity God made, I think the nature of worship played a role in the sort of humanity God made.
Remember, sin is not just disobeying God, it is the love and worship of something other than God. The devotion, allegiance, obedience, and affection that should be God's is turned to something (or someone) else. So while God did not make us sinners (nor did he create sin), sin happens when we put anything else in God's place. We remove God from the throne in our hearts and place ourselves there.
So perhaps God did not make us linked to Adam in our sinfulness just because he wanted it that way. Maybe, in order for the imputed righteousness of Christ to be a possibility, mankind must be of the nature that the imputed sin of Adam was a reality. And this, then, is one reason people don't like the idea of the imputed righteousness of Christ. It presupposes the imputed sinfulness of Adam.
Perhaps God made us this way because it must be so in order to have the sort of worshippers he desired. The nature of freedom required the potential for a fall, and the nature of worship required the potential for slavery to sin. Perhaps the nature of our relationship to sin is the way it is because that's the way God desired our relationship with him to be. At least that's my theory right now.