And bringing death and suffering upon the whole human race, for just one act of disobedience is way way too much where the punishment doesnt Equal the offence. Total Injustice...
Agreed, if God brought death upon the whole human race, that would be injustice. But, Adam disconnected from the source of life before procreating. Thereafter, Adam could only reproduce other disconnected life subject to decay... like his own.
We are born children of Adam and are like him, That is why Jesus three times told Nicodemus that a person must be "born again" if they wish to have a different inheritance from a different father other than Adam.