The average Christian when asked about the root cause of evil in the world or the root of man's problems or the root of God's disfavor with humanity typically cites "the fall" as cause. This amorphous citation is actually not the only cause for the sin in the world according to the Bible. In fact, there is no evidence suggesting that God regretted making mankind after the fall until Genesis 6:6. But, the location of Genesis 6:6 to surrounding material indicates that God considers the actions of the giants in Genesis 6:1-4 a more proximate cause for God's resetting the earth with the flood. While certainly people are the cause of their own problems, the Bible and its writers considered evil spirits a substantial factor contributing to depravity in the world.

This tends to show that the actions of the giants/watchers and the sons of God had a profound impact on the way God approached humanity. Importantly, the first time that God felt the pain of sin resulted not from the sin of man, but from the sin of the sons of God and the watchers and giants. The word for the sorrow of sin brought to the woman, man, and all mankind in the preceding chapters of Genesis is a noun (itzabon). See Genesis 3:16-17; 5:29. The writers used a related verb (atzab) for the word sorrow in Genesis 6:6 to describe the pain that God felt over the depravity of mankind caused by the watchers.

The sins of the watchers are unforgivable, the sins of mankind are. The watchers in an attempt to escape judgement, attempted to pollute and corrupt mankind.

Apparently the original sin of Adam and Eve was not enough to make God regret making more humans, but the supernatural evil was.