Noah's Ark: Its Purpose

For this week, I’ll discuss the story of Noah’s Ark, since the new movie ‘Noah’ just premiered in theaters. 
So, the purpose of Noah’s Ark was for the Lord God to begin anew with His project of mankind on planet Earth, i.e. to ‘wipe the slate clean’:

“The LORD saw how great man's wickedness on the earth had become, and that every inclination of the thoughts of his heart was only evil all the time. The LORD was grieved that he had made man on the earth, and his heart was filled with pain. So the LORD said, ‘I will wipe mankind, whom I have created, from the face of the earth--men and animals, and creatures that move along the ground, and birds of the air--for I am grieved that I have made them.’" – Genesis 6:5-7 (NIV).

 There are many issues I have with this story that I thoroughly discuss in my book (such as why did He decide to include the innocent animals, creatures, and birds in His physical genocide?), but for now, I will pose a single question:

What problem did Yahweh solve if, after the flood, He states, “Never again will I curse the ground because of man, even though every inclination of his heart is evil from childhood.” – Genesis 8:21 (NIV)?

If God’s intention was to help His children with eliminating the wickedness that ‘every inclination of the thoughts of [man’s] heart was only evil all the time’, it does not seem that His solution was a success, since even after the flood and saving the righteous Noah and his family, ‘every inclination of [man’s] heart is [still] evil from childhood.’

The only problem the omniscient, benevolent, and loving Yahweh could have solved in His ingenious solution of physical genocide was His own grief at having created man. That seems rather selfish (and even immature) of Him, and does not characterize Him as ‘just and merciful’, since He did not seem to help to save mankind from our evil inclinations in that particular event.

So the main question is: What benefit did the Lord give to mankind in His relief of grief?