And God saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually. And it repented the LORD that he had made man on the earth, and it grieved him at his heart. And the LORD said, I will destroy man whom I have created from the face of the earth; both man, and beast, and the creeping thing, and the fowls of the air; for it repenteth me that I have made them.
Contradictory – In 8:21 he promises to never destroy the earth (by flood) because of the exact same reason (man has evil in his imagination). Also, God repents/regrets in this verse.
Injustice – God decides to kill everything, man and animals, because man was exactly as he was created. Even if man is to blame, the rest of the planet did nothing.