Orthodox Christianity believes we inherited a sin nature from Adam and because of Adam's sin, God allowed the curse. A person becomes accountable for their decision to sin at a certain age. Because God gave the age of those over 20 years of age for those who were condemned to wander in the desert.
This is why we universally believe that children who die in their original sin are not yet accountable, and get the fast track to heaven. The Jews that were over the age of accountability required a blood sacrifice to cover their sins. Hence the institution of sacrifice by God when He killed an animal to provide clothing for Adam and Eve. He also rejected the non-blood (agricultural) sacrifice that Cain offered for his sins, where as He accepted Abel's blood sacrifice from one of his flock.
God provided His Son to wash away the sins of believers in an eternal covenant with those who have Jesus Christ as Lord. Christ's innocent blood was shed to make restitution for our sins, so that we could reestablish fellowship with our Creator, and attain eternal life!
THis makes no sense. If they'd lived, they'd have been sinners like everyone else. Why the preferential treatment?
You use the word "accountable". Why should we be held accountable for a failure that is unavoidable by nature... (design? ;) ) God might as well hold us accountable for breathing. You still haven't answered that basic question. You just replied with an exposition of Christian doctrine. Not the logical or moral basis for it.