The "sons of God" was a reference for Israel's family tree in the Bible.
Luke 3:38 Which was the son of Enos, which was the son of Seth, which was the son of Adam, which was the son of God.
Jesus reproves any notion that God would join angels, let alone fallen angels in a marriage.
Matthew 22:29 Jesus answered and said unto them, Ye do err, not knowing the scriptures, nor the power of God. 30 For in the resurrection they neither marry, nor are given in marriage, but are as the angels of God in heaven.
One of the most often overlooked point in scripture is the fact that these sons of God were taking these women as wives unto them.
The sons of God would have to be of the godly line of Seth if God in His words were to join these women to be called wives to them in the Bible.
Genesis 6:1And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them, 2 That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose. 3 And the Lord said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
The Lord was striving with man, not fallen angels, and the result was that He had lessened their days to 120 years.
Remember the genealogy of how long these saints leading up to Noah had lived? This was God punishing the godly line of Seth that married outside of that lineage, otherwise, they would have lived as long as Noah.
The reason God flooded the earth was because of this reason along and not because of some diabolical plot to pollute the bloodline to prevent Christ from being born.
Genesis 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. 6 And it repented the Lord that he had made man on the earth, and it grieved him at his heart. 7 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.
Again, it was sinful man having wicked imaginations from his youth that grieved and provoked our God.
Genesis 8:20 And Noah builded an altar unto the Lord; and took of every clean beast, and of every clean fowl, and offered burnt offerings on the altar. 21 And the Lord smelled a sweet savour; and the Lord said in his heart, I will not again curse the ground any more for man's sake; for the imagination of man's heart is evil from his youth; neither will I again smite any more every thing living, as I have done. 22 While the earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.
That's two accounts for the real reason God had flooded the earth.
If you consider how Israel was not to marry outside of the nation of Israel, then you can see why the sober lesson for the cause of the flood was to be taken to heart.
The word "ben" in Hebrews means builder of the family line from which "sons" was translated from.
Believers in Jesus Christ are now called sons of God by the seed of Christ.
John 1:12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: 13 Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
There was necessity to succinctly differentiate from the bloodline because Israel was considered the sons of God formerly as found in the Book of Job when twice at a gathering when Satan was there, Job was picked out from among the sons of God as they were presenting themselves to the Lord.
But getting back to what is relevant to us today:
Romans 8:14 For as many as are led by the Spirit of God, they are the sons of God. 15 For ye have not received the spirit of bondage again to fear; but ye have received the Spirit of adoption, whereby we cry, Abba, Father. 16 The Spirit itself beareth witness with our spirit, that we are the children of God: 17 And if children, then heirs; heirs of God, and joint-heirs with Christ; if so be that we suffer with him, that we may be also glorified together. 18 For I reckon that the sufferings of this present time are not worthy to be compared with the glory which shall be revealed in us. 19 For the earnest expectation of the creature waiteth for the manifestation of the sons of God.
God created kinds to reproduce after their own kind. That includes mankind.
Psalm 127:3 Lo, children are an heritage of the Lord: and the fruit of the womb is his reward.
He can make the woman barren or bear children as all the fruit of the womb is from the Lord.
That means fallen angels did not have a chnace in the first place to pollute the bloodline.
What causes giants? Maybe that is the price that is paid when marrying outside the godly line of Seth that resulted in lessening their days to 120 years. Obviously, they were not to be envied as God is no respector of persons.
So that is the talent the Lord would have me share, but only He can enable anyone to receive this as truth.