It is so strange, in fact, that skeptics use it to show how silly the superstitions that birthed these stories were. They say read the story. You'll find a world far different from the world of reality. Angels have sex with human women and those women have children who were giants. That has to be myth.
But does it really?
In Hebrew the passage in Genesis 6 reads literally thus:
"It came to pass that when Adam (mankind) began to multiply on the face of the land (hadamah) and daughters were born to them, the sons of the mighty ones (elohim) saw the daughters of Adam (h'adam) that they were beautiful. They seized them to be wives, whomever they chose. And Yahweh said, 'Indeed, my Spirit will not always strive with Adam (b'adam) for he is flesh (metaphorically, lustful). His days will be 120 years.'"Notice several words.
First, it is mankind (b'adam) that God has an issue with, not angels. There is no suggestion that angels were judged for this.
Second, the word often translated "sons of God" is elohim. That word is variously used for God himself, for angels, and for mighty ones, rulers, judges, etc. Literally it means strong ones since it is plural. But the context determines the meaning. Here it must mean men because it is men who are judged for this sin.
Because these "sons of God" seize beautiful women to be their wives, it implies that these "sons of elohim" are capable of marrying women - no suggestion of angels being capable of this - and having children by them. It also is implied that it is the seizing that is the crime and not the fact they the "sons of God" were angels. The narrative goes on:
"Nephilim were in the land (eretz) in those days and after that when the sons of God (elohim) came in to (had intercourse) with the daughters of mankind (adam). And they bore to them mighty men (could also mean warriors) who were of old men of renown (or infamous men)."Notice the word nephilim. It is very seldom used in the Bible. In one use it refers to men who were described as large. The word nephim is therefore often translated "giants". But the word is not necessarily denoting giants. It is denoting strong warriors.
In the Genesis 6 passage nephilim are described as being in the land prior to the mighty ones (sons of God) marrying women whoever they seized. They are not necessarily the sons of these unions. The sons of these unions were described as infamous tyrants not nephilim.
If we read the passage in Genesis without the background of translations that cast the sons of God as angels and the nephilim as giants, it sounds not at all incredible. Powerful men ruled the land. They seized women to marry according to their lust. And they oppressed those who lived in the land. This is not a myth.
This sounds like simple historical description. It sounds like the CBS evening news.