Genesis 6:5-6 5And 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. 6And it *repented the Lord that he had made man on the earth, and a grieved him at his heart. (repented/ The Hebrew.root means "to be sorry" moved to pity" have compassion") Let's go back to " that every imagination of the thoughts of his heart was only evil continually" He was also saving all of the children by making sure that they wouldn't grow up in such an evil place because children are very impressionable and so they would go with the flow of society and thus do evil as well. Everyone had their agency but you forgot that there are consequences for every action we do. Example you are always mean to a dog and beat it the dog will end up hating you and may bite you. They had been told what not to do but deliberately disobeyed so the consequences followed. And later God said he would never flood the earth again (Genesis 8:11-13)