The Nephilim account in Genesis is utterly ridiculous when you consider that angels are sex-less beings and would therefore lack sex-drive and romantic attraction. Think of how difficult it is for humans with a sex drive to be sexually attracted to animals. Now take away that sex drive and it becomes literally impossible. So how could sexless angels notice that the daughters of humans are beautiful and have a desire to sleep with them? It make no sense. It is clear that the writer is ignorant of biology - ignorant of the tight link between biology and sex drive - or he would know that there's no way for genderless and sexless angels to be sexually attracted to humans.
Additionally, how/why are these angels able to produce offspring with humans? Are we supposed to believe that the angels took such great care to construct materialized bodies that are human right down to the level of creating compatible DNA with the right number of chromosomes to ensure offspring can be produced? That would mean that their chief concern was not lust but reproduction. But the text implies that it was lust.
The whole story should seem utterly ridiculous to anyone with a rudimentary knowledge of biology. I think this is perhaps one of the more under-mentioned and under-ridiculed stories of the bible.