There are so many compelling objections to the fallen angels interpretation of Gen 6.1-4 that I think their overwhelming sum renders this erotic view fallacious, if not absurd!
First, Gen 6.2 says “the sons of God” took women “as their wives.” Wives necessarily presupposes a domestic life together. Yet advocates of the fallen angels interpretation ignore this concept by only positing angels having sexual intercourse with women.
Second, this fallen angels interpretation is a male chauvinistic view of angels. How so? It presumes that all angels have male sexual organs that produce (physical?) sperm compatible with human procreation. Yet the Bible never says this. Moreover, the Bible repeatedly identifies “angels” as “spirits,” sometimes interchanging these two terms. And the Bible never says angels procreate their own species.
Third, while the Bible often describes angels appearing visibly to humans as men, such texts likely only mean that angels appear human generically, not that they are human.
Fourth, the Bible’s first creation account—in which God tells a select group of angels he will make human beings in “our” image—adds that he will make them “male and female” (Gen 1.26-27; 5.1-2). This suggests a contrast in which God and angels are sexless. The primary divine purpose for making humans male and female, not to mention animals, was for them to copulate and thereby reproduce their own species to populate the earth (Gen 1.27-28). Trinitarians interpreting “us” in these texts as support of their doctrine is eisegesis rather than exegesis.
Fifth, Jesus indicated that angels are sexless when he said of God’s people, “in the resurrection they neither marry nor are given in marriage, but are like angels in heaven” (Mt 22.30; cf. Mk 12.25; Lk 20.35-36; cf. Gal 3.28). Jesus clearly meant angels cannot propagate. Many NT scholars rightly claim that this saying of Jesus is the foremost biblical text that dispels the fallen angels interpretation of Gen 6.1-4.
Sixth, Gen 6.1-7 blames only humans, thus not angels, for this wickedness. For we read, “the wickedness of humankind was great in the earth, and that every inclination of the thoughts of their hearts was only evil continually” (Gen 6.5). And twice the text says all flesh was “corrupt,” and “the earth was filled with violence” (vv. 11-13). Thus, God was going to destroy both men and women with the flood since both had sinned. This exclusive blame of humans may be the second strongest counter to the fallen angels interpretation of Gen 6.1-4.
Seventh, it is unjust for men to suffer the judgment of the flood if they were not involved in the transgression committed, in which only women copulated with angels.
Eighth, this fallen angels interpretation is presented as though the women could not resist the angels impregnating them, which makes the women blameless as well.
Although Genesis 6 only blames humans for the wickedness that caused God to destroy the earth by a flood, 1 Pt 3.18-20, 2 Pt 2.4, and Jude 6 fix the underlying cause of it on the influence of angels. It resulted in God casting them into the underworld’s Tartarus to await their final judgment. These verses are obscure to us moderns since their authors treat a matter unknown to us that raises questions. This suggests that these matters were known to most first century Jews or else these authors likely would have said more about it. If so, they may have used common oral, if not written, tradition that afterwards became non-extant. This is supported by (1) the last two passages fitting the same order of the destruction of the earth with a flood and the destruction of Sodom and Gomorrah, (2) angels deemed partly to blame for the evil, and (3) similar language or concepts are used. These texts help interpret each other, such as the spirits in prison being angels cast into hell, and these angels disobeying God since they “did not keep their own position, but left their proper dwelling.”
To sum, although “the sons of God” in Gen 6.1-4 were men, thus not angels, who took women as wives and procreated with them to produce Nephilim, three NT texts seem to blame some angels for influencing these antediluvian humans in committing this wickedness which caused God to judge the entire world by sending a great flood that destroyed them all except for righteous Noah and his family.