What purpose did the Flood serve besіdes proving that god was an utter failure at ridding the world of evil?

Man has free will. It is up to you with how you behave good or evil. It is up to you to chose if you believe in God and live according to the bible. He does not blame us for our imperfections, He forgives us time and time again. But since your questioning and blaming God for everything...What is your and man's responsibility and role in what you call a global screw up???