"It is interesting to note that God destroyed a world because of Genetic contamination. At Genesis 6:1-4 the account says,
When men began to increase in number on the earth and daughters were born to them, 2 the sons of God saw that the daughters of men were beautiful, and they married any of them they chose. 3 Then the LORD said, "My Spirit will not contend with man forever, for he is mortal; his days will be a hundred and twenty years." 4 The Nephilim were on the earth in those days and also afterward when the sons of God went to the daughters of men and had children by them. They were the heroes of old, men of renown. (NIV)
The result of this union of angels and women is shown in the verse 4. Peter shows that this act was disobedience on the part of the angels in 1 Peter 3:19,20,
through whom also he went and preached to the spirits in prison 20 who disobeyed long ago when God waited patiently in the days of Noah while the ark was being built. In it only a few people, eight in all, were saved through water, (NIV)
He mentions these angels again in 2 Peter 2:4,5 and also Jude at verses 6,7. Jude shows that these angles, and what they did can be compared to what Sodom and Gomorrah did. While of course the men of Sodom practiced unnatural sex, and also had lust (wrongful lust toward women) These angels had the same attitude, and feelings, but toward a strange flesh, that is, other flesh, because they were not flesh. They wanted to mingle with human flesh. A commentary on 1 Peter written by Kenneth S. Wost quotes from Dr. James H. Emgray who suggests the possible purpose of Satan, in this angelic in rode into the human race. He says, " A confounding of two distinct orders of creatures, and production of a mixed race, partly human, and partly super human which would be just such a derangement of the divine plan as to distort that which accrued namely the almost total extermination of all who are upon the earth". Then Wost makes some comments which we will paraphrase here, Now connecting this with the fact that our Lord after His death made a proclamation to these fallen angels, we suggest that the probable purpose of the angelic apostasy so far as Satan was concerned, was thederangement of the of the divine plan of the substitutionary atonement of the Son of God. For if his purpose had succeeded, God's Son would not have put himself into a race part angle, and part man. Christ was to answer in his humanity to the humanity of the first Adam. The action of God completely exterminating the human race, and saving Noah and his family, prevented the spreading of this unlawful mingling of this angelic and human natures. The proclamation Christ made to these spirits in prison was probably to the effect that with his dying as a ransom for Adams offspring, completing his ransoming work, He had defeated the plan of Satan to defeat his purpose. It would therefore be a proclamation of victory. Now it has been said of these angels, rather the offspring of these angels and women would be sterile for their highbred. There is absolutely no proof of this. Apparently, with God's purpose in view He created the human race a procreated race. Unlike the angels who were created directly, and apparently individually. This would make it possible for Christ to become human, and die for all humankind, for as in Adam all die so in Christ should all be made alive. Christ the first fruits when he was resurrected, and those who are Christ at his second coming. These will be his brothers, the church his bride."
This is taken for a PDF I downloaded once, but I can’t find the link where I downloaded it from. My understanding is that it was written by Edward Dunlap. I’ll see if I can find it…