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Depends on your definition of ethical. Assuming you define it in terms of a lack of cruelty to the animals and their handlers then such meat does exist.
However, the vast majority of meat is not that. The issue is it's cheaper to produce meat unethically than it is to produce it ethically. Because of that, at every step in the production to mouth there's a strong incentive to go the cheap route rather than the ethical route.
But doesn't this depend upon your definition of cruelty? I've seen vegans who define raising an animal for the purpose of eating it to be inherently cruel, even if it doesn't suffer any negative treatment until the day it is killed to be eaten.
Even this is just going with common enough definitions found in modern society. If we expand our scope of what ethics and what views of cruelty are allowed, there is no end to what results we see.
It really just comes down to definitions.
https://journals.plos.org/plosone/article?id=10.1371/journal...
Which sort of makes sense when you consider our closest relatives are primarily plant eaters.
Our ancestors have shifted to a diet with a large percentage of animal fat and meat, which has lead to a simplification of our digestive system, for more than a million years.
Only during a little more than the last ten thousand years there has been a reverse shift towards a lower percentage of animal food, most likely after we had exterminated most suitable wild animals, which forced us to become creative and discover agriculture, otherwise we might have become extinct, like our prey.
Now, with our reduced digestive system, we could not live eating the kind of plants eaten by a gorilla or even by a chimpanzee. We need much more nutritious food, which can be provided only by plant seeds, the only parts of plants that are rich in proteins.
What they're actually doing is measuring the isotopes in the carbon of the bodies of the human remains. You don't get any carbon in your body from the water or from the fiber in plants.
So your estimate correction needs to go the other way - the study says that > 80% of carbon in the bodies of early human foragers comes from plants. That means that also > 80% of the caloric intake comes from plants. Or alternatively, it would mean that > 95% of what they ate (by weight) was plants.
I'm with you that the collective we is fat and stupid and would go further than our various systems and patterns solve for predatory behavior against both humans and non-humans leading to those outcomes, and it is super unfortunate.
0 is a great number for rich countries to aspire to. Without some sort of massive crisis (which we're heading towards globally) it would probably take at least 100 years to even halve the current consumption levels. It took roughly 100 years to go from an average of 10lbs of chicken consumption per year (1920) to the current 70lb average (2020). Chicken is really where all the growth for meat consumption has come from.
Beef has been fairly steady per capita, and has decreased from its height a few decades ago — but the population keeps rising so it can't continue like this.