I think history indicates the opposite view, unless one goes back many millions of years to our more primitive, largely vegetarian primate ancestors. After those early vegetarian-like days, humans evolved to eat meat often, and we are still adapted for doing that. Those were the classic hunter/gatherer days, which lasted for hundreds of thousands of years, and adoption of agriculture was only about 10k years ago. Before agriculture, humans hunted wild meat often, as needed, and their population was small enough that the natural ecology could support that lifestyle.
This started when one of our ancestral species several million years ago discovered how to make a flint blade by banging rocks together. They used those blades to scrape off the bits of meat leftover by predators on the bones of their kill.
This resulted in a major increase in the protein in their diet. The extra protein allowed their brains to grow larger. (Brains require a tremendous amount of protein for maintenance, which is why dogs, which have been bred to be scavengers, have smaller brains than wolves, which are hunters.) So eventually a species arose with a larger brain, and these people invented even more powerful hunting tools such as spears, and techniques such as cul-de-sacs. So their diet was even richer in protein, and their descendant species had an even larger brain. Eventually our species,
Homo sapiens, arose, and we figured out how to domesticate animals so we had a huge supply of protein living right in our backyard.
It could be argued that humans are
obligate carnivores, since we could not survive on a plant-based diet before the technology of cooking was invented, which makes the protein in grains and legumes digestible. We are certainly the
apex predator on this planet, dining on the flesh of both bears and sharks.
It was not until the spread of cities, around 5000BCE, that meat began to be hard to obtain. The cities were growing so large that it was not easy for the surrounding pasture land to
produce enough meat for the inhabitants and
deliver it to them with no refrigeration or motorized vehicles. At this point humans began to rely more on grains for their protein, and nutritional deficiencies began to reduce our life expectancy. Grains have protein, but they don't have all the vitamins and minerals we need. The fruits and vegetables that have these nutrients are not as easy to grow in mass quantities as grains are, and they also spoil much faster.
I agree with your sentiment that we should try to phase out carnivorism, especially that which involves eating mammals, for the sake of humaneness. Then, soon, I'd like to remove fish and poultry from our diets after we establish substitutes with better nutrition than even those.
There's nothing wrong with being humane and ceasing to kill animals for food, even though some of us are of two minds on the subject and can't imagine living without meat. We'll certainly be dead long before this happens so we don't have to worry about the conflict.
However, dairy products (milk and eggs) have almost exactly the same nutritional content as meat. Moreover, dairy farming is an enormously more efficient use of pasture land that meat farming: one acre of land used to graze dairy cows produces ten times as much food as the same acre used for beef cattle.
We should have no qualms about putting cows to work producing milk and chickens to work laying eggs, so long as they are treated humanely and not warehoused in today's "factory farms." Everyone has to work for a living and there's no reason why that can't apply to non-humans, as long as we treat them as kindly as human workers--or maybe even a little better.
