We can observe that humans are omnivores and eat other animals for sustenance. Why do we not eat each other?
Other animals eat each other. Over 65% of male spiders when they mate will sacrifice their body to the female. And she will eat them. Praying mantises eat each other too. I remember from Kung Fu Panda that Mantis said something about him being eaten by a lovely woman mantis or something like that. Tiger sharks will eat each other too. Animals all throughout the animal kingdom will eat each other.
We can infer that by eating each other, these animals either do not know they are eating something from their own species or that they just don't care.
For more primitive animals like insects and spiders, I think the mental capacities are too small for them to know what a species, much less to care. However, for tiger sharks, they just eat whatever they want and don't care.
But not all other animals eat each other. Lions, humans, koalas, and other more intelligent animals do not eat each other. This may be because these animals are smarter and can recognize moral problems with cannibalism. For non-human organisms though, I don't think that is the case.
I think these other animals that don't participate in cannibalism due to the communal nature of living for lots of these animals (lions in packs, koalas in koala groups, and humans in societies). These animals can recognize others of their species and will refrain from cannibalism because they have more complicated memories and can connect the image of a dead corpse of their species to positive memories associated to spending time with others of their species.
Humans don't eat other humans for the same reason. We spend our whole lives growing up and living with other humans so the idea of eating a human corpse repulses us. Our identity is so based on and connected to other humans that we just don't like the idea of feasting on human bodies.
I don't know for what reason but everyone says that red meat (cows and pigs) is unhealthy. I personally don't care much about this because I love beef so so much but it is important to consider for the sake of argument.
Cows and pigs are closely related to humans genetically. We share 98% of genetic material with pigs and over 80% of genetic material with cows. Chickens on the other hand, only share 60% of our genetic material. Plants share probably even less of our genetic material. We are so fundamentally different from plants on a cellular level that I don't even really want to look up the stat on how closely related we are to plants.
Vegans and vegetarians say that it is healthier to eat plant based things, or in other words, things that are further genetically related to us. Chickens are more genetically distant from us than pigs and cows and eating chicken is supposed to be healthier than eating red meat.
Hmm...
This means that the further away genetically something is from humans (plants), the safer it is for us to eat. The closer genetically something is to us (cows and pigs), the more dangerous it is for us to eat.
That naturally explains another reason why humans don't like to eat other humans. If we were to eat humans, we'd be eating things with 100% genetic similarities to us (obviously) and that would be the worst possible thing for us to eat, health-wise, by this logic.
Ok so this is my first post in Deep Thoughts. I think this section of the website will end up being quite interesting. Please let me know your thoughts and give me feedback. Thanks for reading!