Well, sex with monsters stories can be seen as a reflection of cultural fears about boundaries. In a cultural context, there are proper boundaries in relationships, and when these are violated, as in the case of having relations with non - human monsters, it can represent a fear of chaos. It's like a warning about what could happen if we don't stick to the norms. Also, it might show the fear of losing our humanity. If someone engages with a monster sexually, it can be seen as a step towards becoming less human, which is a deep - seated cultural fear.