Source: George W.E. Nickelsburg, "The Bible Rewritten and Expanded," Jewish Writings of the Second Temple Period, ed. Michael E. Stone (Philadelphia: Fortress, 1984) 92.
"The Semihazah story in I Enoch 6-11 is an apocalypticized retelling of the Genesis story, and the author's restructuring of the biblical text and his mythical view of reality have counterparts in apocalyptic texts from the time of Antiochus Epiphanes. The Semihazah story must be dated before the second century B.C.E. and perhaps as early as the wars of the Diadochoi (323-302 B.C.E.)."
In I Enoch, giants wreck havoc on humanity, as evil angels teach people their wicked arts. I Enoch is embellishing Genesis 6 (though I've read some who see Genesis 6 as a condensed version of I Enoch's legends). Is I Enoch a critique of Hellenism here? The Gentile powers liked to throw their weight around, which resembles the giants. And they introduced Hellenism into Judea, which many believed undermined the traditional Jewish culture, as the evil angels corrupted the human race.
If this is the case, how did the author of I Enoch view the story that he was writing? Did he think it was an allegory, in which the giants and the bad angels were symbols of the Hellenistics powers? Did he believe things really happened that way prior to the flood, and that the things that occurred back then could guide the Judeans in the time that he wrote? Did he consciously make up the details of his story, or did he simply believe that he was interpreting the Genesis text, not making anything up? Sometimes, we interpret texts based on our historical contexts, and we may unconsciously make things up as we do so.