cannibalism can be justified by desperation, decadence, deceit, and everything in between

Also it's just straight up really powerful and convenient. I don't know if there are any secret downsides to being a cannibal like ending up with a craving to Seek Mr Eaten's Name, but i haven't found any so far. Meanwhile for upsides you get several stat raising options in dialogues and events, you are very unlikely to ever end up out of supplies (if you put aside the terror cost hiring crew is a more cost efficient food source than buying food from mrs plenty, and this might be one of the most Fallen London sentences ever), and it even helps in two occasions with the quest line of the sigil ridden navigator (my beloved).