The point is for you to understand how bad sin is. God punishes disobedience against Him severely because that is how bad it is. You are not the one to make judgments about how bad sin is. You did not create the universe and everything in it.
Also a human ruler is not a correct comparison to God. A human ruler is a sinner himself. God only is without sin, and His punishment on our willful, knowing sin, after we had been blessed with perfection and bliss in the garden, is His own to decide.
I believe every word of the Bible is literally true, but it's obvious there is an allegory here to each one of our lives. We are not being punished because we are only descendants of Adam, as if we ourselves had never sinned. We share the same nature as Adam and are rebellious ourselves, therefore deserve the same judgment. God's infinite kindness is accepting this punishment on Himself in order to save those of us whom He chose.
And as to those He did not choose, Joshua 11:20 would suffice, "For it was the Lord's doing to harden their hearts that they should come against Israel in battle, in order that they should be devoted to destruction and should receive no mercy but be destroyed."
Or Romans 9:20-22, "But who are you, O man, to answer back to God? Will what is molded say to its molder, 'Why have you made me like this?' Has the potter no right over the clay, to make out of the same lump one vessel for honorable use and another for dishonorable use? What if God, desiring to show his wrath and to make known his power, has endured with much patience vessels of wrath prepared for destruction, in order to make known the riches of his glory for vessels of mercy?"
Not all are chosen by God to receive the free gift of spiritual rebirth. Those of us who have been so chosen will show the fruits in our lives as we are regenerated, as no good tree bears bad fruit, and God changes our nature to the core. I believe even God's chosen have the free will to reject that gift, as did Judas.