Years ago I thought the reason we didn't kill certain animals is they're cuter than others. Maybe, but there's a perceived scale of demonstrated consciousness. If an animal appears more intelligent and compassionate (e.g. chimps), we're more put off on slaying them.
https://www.sciencedirect.com/science/article/abs/pii/S16165...
When I ate dolphin I didn't know it was dolphin. It was so good. Then I found out it was dolphin. I think no one should eat dolphin because if they do soon dolphins will be extinct because they are that yummy. Dolphins don't do well in captivity and haven't been domesticated. So we can't just ramp up the number of dolphins. Eating them is a real risk to their survival as a species.