God is Master of the Universe. As such, he has the right to make rules and HE gets to decide consequences of disobedience--and he also rightly defines what is right or wrong.
But only 1 disobeyed.If I run through a red light, should you get the ticket also? Also, why would imperfect people pay for the error of a perfect person? I agree that Adam broke God's law, and HE should have some sort of penalty.