I've always felt that monsters are representatives of social dread and political conflicts. Because they're able to use monsters as allegories for these fears, horror films can touch on dangerous issues in a way that standard dramas can't or won't.

If you're a social outsider either by choice or default, monsters end up becoming very attractive because they want things they aren't allowed to have. In order to get them, they don't mind making a mess out of those "normals" who stand in their way.
Tell me where the Blood Red River runs/ From my back door to the rising sun/ On again away till dawn/ Never straight and way too long