Hrcho, we must not indeed redeem the sins of our father/mothers. I want to distinguish doing sin from sin in general, which is missing the essence which has God given to us. Due to sin, we have become sinners. I realy believe Adam is a representative for menkind in general. Oh and I never said it was easy or anything. See the choice of Adam as the breaking of the world, like the closing of Valinor. Ever since, the entrance was shut and only due to the whole sacrifise cermonies and the strict laws people were reminded by the existance of God.
Why would people else need Christ? Even as a non Christian, that knows anything about Christian dogmatics, should be able to answer that question. What was it he should have made right? Only for Adam and Eve? Only for the real bad people?
Like I said, the simple fact that the world is pretty messed up. Ending recources, aid for those who need it always slowly. People denied food, safe water and medicines. People enriching themselves. And the list could go on for ever. That, to me shows the world needs redemption.