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.
6:5 only evil continually. Universal wickedness requires a universal cause adequate to produce it. Nothing less than a worldwide influx of demonic control seems adequate to explain it.
6:11 filled with violence. In order to be “filled” with violence, the earth by this time had become filled with people.