1) It is the most natural way to interpret the passage.
This follows the “golden rule” of hermeneutics; when the plain sense of Scripture makes sense, seek no other sense, lest you end up with nonsense.
2) Because of a statement in Matt. 22:30.
This verse implies that angels do not merry. While it may be argued that they should not marry, I find no reference in Scripture that indicates that angels have ever married, reproduced, or even desired to do so.
3) Because of the law of biogenesis-life begats similar life.
This is clearly spelled out in the creation account. How could an angel reproduce with a human? If the angel took on the form of a man, what would his offspring be, man or angel? If the angel merely possessed a man, then it is no longer angels cohabiting with women, but men with women.
4) Because of Paul’s statement in 1 Cor. 15:35-40.
These verses are emphasizing that there is a difference between earthly bodies and heavenly bodies, and it is a distinct difference.
5) Moses did not us malak for angels.
This is the normal Hebrew word for angels, used almost 30 times in the Pentateuch.
6) Because “mighty men” is the Hebrew word gibbor.
A point of significance with those who hold that the sons of God are fallen angels is that their supposed offspring were “mighty men”. Yet this word is used over 150 times throughout the Old Testament. Should we conclude that Gideon, Saul, David, Boaz, and even God Himself are the offspring of fallen angels and women since this word is used in reference to them? Obviously not!
Those who hold to the view that the sons of God are fallen angels generally support their arguments along the following lines:
1) The Hebrew phrase bne-elohim (sons of God) always reefers to angels in the OT.
To my knowledge, this word is only found six times in the OT. (Gen. 6:2,4; Job 1:6; 2:1; 38:k7; Hosea 1:10). While five of the six seem to clearly be reference to angels, Hosea 1:10 is obviously a reference to the children of Israel. Another observation to be noted is that in the book of Job the sons of God are seen to be faithful angels with Satan coming in among them. The reading leaves you with the impression that he is out of place, that is, he does not belong there. If Gen 6:2,4 are references to fallen angels, then it is possible the only place Scripture uses that phrase to refer to fallen beings, whether men or angels.
2) The Hebrew word nephilim actually should be rendered as “fallen ones”.
Nephilim means a feller. It is a masculine Hebrew noun with roots meaning to fall. Whether nephilim is a fallen one or one who causes the fall of others, such as a bully or tyrant, is debatable. The word is used only 3 times in the OT, here and twice in Num. 13:33 where it is used in reference to the sons of Anak who were apparently much larger than the 12 spies. Is the possibility that these men were unusually large sufficient reason to conclude that they were the offspring of fallen angels? Where does that leave Goliath? Or David’s mighty men of valor? Or, on the opposite extreme, pygmies, who are unusually small? This type of conclusion seems without basis and beyond the realm of reason to me. Why can’t the Nephilim simply be fallen men who are “big, bad, and ugly”?
3) Because of ancient pagan legends.
While there may be some truth to ancient legends, they are still legends and are poor guides to use in understanding Scripture.
4) Because of the common opinion of Jewish writers.
This is perhaps the best case for this view, especially if the Septuagint translates Gen. 6:2 as “angels of God.” However, while history is important to consider, it is not the determining factor in interpreting Scripture.
6) Because of the interpretation of the early Church.
Here again it is important to consider the views of the early church, but, their interpretation was probably colored by the reading of the Septuagint.
In conclusion, let me reiterate what I stated earlier; I see no need to look for alternate meanings to this passage when the normal reading of it makes sense. In Gen. 5, we see listed for us the descendents of Seth, the God-honoring line of Adam. It seems to flow quite naturally into chapter 6 as these men begin to intermarry with pagan woman, which results in the statement by God in Gen. 6:3. The point has come when even those who fear God have begun to fall away, and God makes plans to destroy them all. But there was a remnant, one who had not defected, Noah. He found grace in the eyes of God. (Gen 6:8)