still, meat is being pushed as the core diet in these worlds

The natural tension between herbavoires and carnavoires is a major plot point of Beastars. It's primarily used as a metaphor for the tension between age cohorts and genders, but vegans and anprims ahem eat it up, regardless.

Similarly, Attack On Titan is all about humans turning into giant cannibal monsters, then justifying it to themselves.

Also, a very popular trope in Vampire / Werewolf / Zombie settings. "How does cannibalism become socially appropriate?" has become a popular subject of modern fiction, particularly in the horror genre.