The problem relates to the test of obedience given to man by God (Gen. 2:16-17). Who was involved in the decision taken by man - was it only one person (i.e., Adam) as Genesis suggests, or were several, perhaps many, human beings involved? If God chose to give the choice to a group of men, He first would have had to address the following possibility:
What if there were disagreement in the group?
The effects of the alternative choices are incompatible. By the choice of obedience to God, mankind would have been preserved from bodily death and would have lived in a state of paradise upon Earth before entering Heaven. However, by the choice of disobedience to God, mankind was no longer preserved from bodily death, was subjected to inherent sinful tendencies, and has had to live with disease, violence and a harsh physical environment.
It is hard to see how the effects of the alternative choices could be implemented simultaneously. If there were many men, some might have chosen to resist the devil's temptation, while others might have chosen to eat the forbidden fruit, thereby becoming corrupt. How could perfect human couples co-exist with corrupted ones?
And what of the physical environment itself - how could it be a state of paradise for some, while a state of harsh climactic conditions for others at the same time? It seems more reasonable to hold that only one choice could be implemented. If this is granted, then a dilemma for the idea of polygenism must be faced:
If more than one person were involved in the choice and there were disagreement in the group, only one party could have its choice implemented. The choice of the other party would have to be overridden. This would hardly be fair, and the members of the party concerned could feel that God misled them.