The indigenous tribes of the western hemisphere weren't really cannibals. That was propaganda spread by the Spanish. But let's say they were cannibals, it doesn't make a case for eating meat because cannibalizing other humans result in disease. Most animals are hard wired against cannibalism, of course with a few exceptions. So yes they are cannibalistic chimps out there, but when looking at the whole species, plants/insects outweigh the meat consumption. Even dedicated herbivores such as deer or cows will sometimes try meat if they chance upon it. There are records of cows devouring live chicks and munching dead rabbits, of deer eating birds, and of the duiker, a tiny African antelope, hunting frogs.
What we observe eating isn't necessarily what is best. Consuming whatever is bad for you gives you disease and over time kills you. According to WHO, red meat is a probable carcinogen because of things that exist naturally in it, like heme iron. Should an omnivore get cancer from eating meat?
The whole 'meat is needed for protein' is a myth. Let's say you need to get 56 grams of protein per day. If you eat broccoli for a day, you would get 147 grams of protein. Next day if you decide to do lentils, you would get 157 grams of protein. There is protein in corn.
Vitamin B12 is made from bacteria so you don't 'have' to eat meat to get it. A B12 supplement is fine. You only need a little. A B12 supplement benefits may outweigh the risk of a vitamin b12 supplement via meat.
Carnivores, or those that were designed to eat meat, tend to have shorter digestive tracts plus higher acid concentration to break down meat and quickly push it out so it is not just sitting there decaying. Omnivores have digestive acid of a ph around 1 meaning that it can dissolve bone, humans tend to have a ph around 4 or 5. Omnivores trunk to intestinal ratio is 4 to 6 times while humans is 10 to 12; meaning what we eat sits with us a lot longer. Meat that sits in our bodies, decaying, for too long set off a series of inflammatory responses that lead to disease.
I never said the indigenous tribes of the western hemisphere were complete vegetarian. I was saying that their diet wasn't as meat heavy and the animals they ate weren't necessarily living with them (domesticated). They hunted thus limiting contact and cross contamination. Besides being just dirty, the poor hygiene the European had was due to their relationship and handling of animals. As you say, the indigenous tribes had/ate animals too but it was the European getting them sick. What were the indigenous plagues that could get the European sick seeing that the European weren't native to the land? There are those that say Africans might've reached the Americas before the European. If so, the African didn't wipe out the tribes. What was it about the European that was so deadly? Where did their unusual bacteria and viruses come from seeing that the North American climate was very similar to the European?
I do think it is possible that global warming could unleash ancient bacteria and viruses, but that is not what we are seeing with the coronavirus. Both outbreaks have been traced to a particular area in China due to the bringing together of animals from all over the world, the unsanitary and cramped conditions, and the handling of these animals that allow pathogens to jump and mutate.
Plants have viruses too, but it is extremely rare for a human to get sick from it and pass it on.
Yes people have survived plagues and built resistance once half the population died off. But if we can stop outbreaks from happening, we can stop millions of dying unnecessary deaths every so often. Plagues are not natural. I cannot just shrug my shoulders and think 'oh well, at least we'll be better off once it's over because it builds our immunity'. Disease is called disease because it is not natural. What man are doing to these animals before consumption is not natural. And definitely these wet markets got to go.