The poem’s Grendel is a primal force of evil spawned by sinful human nature itself and now perennially at war with the creation. The guilt is not sexual and personal but general in terms of mankind’s instinct toward fraternal violence.
That general guilt gives Beowulf ’s heroism its context. It tells us that evil is woven into human nature, but that individual men may choose to stand against it. The film Beowulf descends into moral equivalence and relativism as Beowulf, in his turn, is seduced by Grendel’s mother, a slinky CGI version of the likewise slinky Angelina Jolie. “I know that, underneath your glamour, you’re as much a monster as my son, Grendel,” she tells him. Which is blithering nonsense. In the poem, she’s the monster and he’s the guy who’s got to kill her so that men may live in peace. That may not be nuanced or urbane or pseudo-deep, but it’s actually more honest, more like life as it is lived. The evils of this sad world are not always susceptible to analysis or negotiation. Some monsters are really monsters and just have to be taken down. That’s why poets write—or used to write— epics honoring the warriors who do the job.