Has anyone seen the movie, "Soluent Green"? It's about the human animals that live in the future. There are huge, secret factories of which the average human is unaware. Everyone eats soluent green which has become the staple for continued human survival. One of the characters in the movie happens to discover that the factories are where the green is produced and that it is actually manufactured out of human remains.
Rendered human corpses. If we continue existing on the corpses of other animals, we might actually arrive at a time where this is necessary.
Marvelous ironic and poetic justice!!!