If you're up to the task, your challenge is to create an ATL, with a POD no earlier than 500CE, where cannibalism in some shape or form is normalized across the Western World, and the world as a whole. To make this slightly easier, let's use Cornell's definition of cannibalism, namely "the nonconsensual consumption of another human's body matter" (and let's also say that neither breastfeeding nor swallowing without your partner's consent during the act of giving oral sex count as proper acts of cannibalism, so that there aren't any grounds on which to argue that it already is IOTL). What would be the most plausible way to go about doing this?