The pig is food. I will eat the pig. I won't eat the human. The pig isn't indiscriminately murdered, it is slaughtered for food. We as a society still think it is morally right to kill someone convicted of a crime in some places. While I don't agree with that, those states do. If morals can be grey, it's because they are. Morality is a human construct. What's moral today can be immoral tomorrow.