Genesis isn't one of my favorite parts of the Bible, one of the reasons being the science versus creationism debate. Sometimes you have to. Last week someone asked me why God put the Tree of Knowledge of Good and Evil in Paradise if He knew that Adam and Eve would eat from the fruit of it and Man would Fall.
Paradise was a perfect place. Adam and Eve had everything they could possibly want. God wanted Man to have a choice, to have responsibility. If you aren't given a choice, it is impossible to have responsibility. This responsibility extends to the choice for or against God.
'But, why did the punishment have to be this radical?', this person replied. In a perfect world, Paradise, it is impossible to steal a cookie. If everything is perfect, without sin, every wrong choice is radical. Every punishment can't be anything other than radical.
After the Fall of Man, God gives Man the possibility to turn around. There is responsibility, there is punishment and there is grace.