Who were the “sons of God” (Genesis 6:2)? Were they fallen angels? Did they mingle with humans and procreate with them? If so, would that cause a super human race (i.e., Goliath)?

[T]he sons of God saw that the daughters of men were beautiful, and they married any of them they chose—Genesis 6:2. Even the commentaries seem split on the identity of the “sons of men,” but there appear to be three basic positions regarding them: (1) they are heavenly beings such as angels (an ancient Jewish position), (2) they are kings or other aristocrats, thus the high class consorting with the lower class, and (3) men from the (assumed) godly lineage of Seth (Adam and Eve’s son following their separation from Cain and the death of Abel). The issue with the idea that the “sons of God” were fallen angels is, according to Jesus, angels do not marry: At the resurrection people will neither marry nor be given in marriage; they will be like the angels in heaven—Jesus Christ, Matthew 22:30. However, since there were already a group of angels who had fallen as a result of alliance with Satan, the possibility of fallen angels having somehow assumed human form to seduce human females is possible. While the idea that they are kings or otherwise upper class is not impossible, the context of Genesis 6 is the grotesquely overwhelming nature of sin that came into the world at that time; as this chapter points out, The Lord saw how great man’s wickedness had become, and that every inclination of the thoughts of his heart was only evil all the time—Genesis 6:5, and therefore The Lord was grieved that he had made man on the earth, and his heart was filled with pain—Genesis 6:6. The most-cited evangelical position, particularly in the context of the chapter, is the third one—the line of Seth (godly) commingling with the line of Cain (ungodly) due to the contrary nature of such unions with God’s will as expressed in Paul’s second letter to the Corinthians: Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness? What harmony is there between Christ and Belial (Hebrew, “wicked, ungodly”)? What does a believer have in common with an unbeliever? What agreement is there between the temple of God and idols? For we are the temple of the living God—Paul, II Corinthians 6:14-16a. It is basically impossible that a super human race would have resulted from relationships between the “daughters of men” and “sons of God” simply because the events recorded in Genesis 6 are events which occurred before the Flood, and we read later on, as a result of the Flood: Every living thing that move on the earth perished—birds, livestock, wild animals, all the creatures that swarm over the earth, and all mankind. Everything on dry land that had the breath of life in its nostrils died. Every living thing on the face of the earth was wiped out; men and animals and the creatures that move along the ground and the birds were wiped from the earth. Only Noah was left, and those with him in the ark—Genesis 7:21-23. Outside of the ark, there were no survivors.