If we added Homer's Illiad with other ancient writings then we could add some really detailed descriptions of what "fallen angels" must look like.
The Children repeatedly demonstrated a reluctance to do what God told them and a penchant for complaining, bemoaning their current condition. They needed a reason to not invade and take over a land they were being told God was giving to them. The inhabitants were tall, big and fierce warriors, yeah giants. Let's go some place where they are not instead. Good idea. Write that down so century laters imaginative people can believe we saw "fallen angels".
The primary verse in question is what the problem is:
Genesis 6:4
4 The Nephilim were on the earth in those daysand also afterwardwhen the sons of God went to the daughters of humans and had children by them. They were the heroes of old, men of renown.
Now, say "the Nephilim" were "just corrupt people". Why are they then called in the very same breath, "the sons of God".
And why are they called "the sons of God" and the women called "daughters of men".
And why is it said that they great children?
There is nothing remarkable about people sleeping together and having children.
There is no sin, nor fallen state for a mortal "son of God" to sleep with even a "unbelieving woman" and have children.
The New Testament says that our children are saved for our sakes by default.
Why would it have been different then.
From what it appears it does not make sense to state that this verse is saying anything different.
As for language difficulties, these are with only the exception of the word "Nephilim" completely ordinary and very often used - and so well defined - words and terms.
Though, perhaps, it is true, the term "sons" used as "sons of God" is only used in one other place in the Old Testament. And that is in Job 1:6 when they are angels spoken of presenting themselves before the throne of God.
This simply then leave the "illogical" problem of what it says is not being normal or possible, according to mortal people. That angels can not sleep with mortals.
But, this is not something based on fact or knowledge, there is no proof anyone has that this is not the case.
One can only make an assumption. Not have facts.
If anyone has personal experience, only then could they have facts. But this is ruled out as well, as it is impossible to prove personal experience to anyone else. So, effectively, one can only make an assumption without facts.
Therefore, that leaves that argument out of the equation entirely except as a intellectual possibility in their own mind.
I, can not absolutely prove the verse says one way or the other, as well, simply that it is not reasonable to argue it seems to say the Nephilim were just regular mortals, or even "fallen" sons of man.
It might also be noted, with the exception of the reference of "sons of God" to angels in the book of Job -- the next time anywhere hears that manner of phrase is when Satan asks Jesus if he is really the son of God.