For the most part of our existense we didn't eat much or any meat. Only when humans invented the farming of livestock we started our journey to the (over) consumption of meat.
Our teeth, nails and inability to easily digest raw meat and other physical properties are also a testament to the fact that we were not designed to hunt and eat meat as much as we think we do.
I don't know where you got that idea. Our teeth are pretty standard omnivorous and we have archaeological evidence of hunting long predating modern humans (we're talking >2MYA).
> Our teeth, nails and inability to easily digest raw meat
As opposed to our ease of digesting raw beans, grains and tubers, which at best we literally can't do and at worse are actively toxic unless extensively prepared?
Humans digest raw meat just fine. Cooking does help a bit but not that much as to suggest it's an evidence for us being herbivorous. It's more about taste and safety nowadays.
I'd suggest you try raw meat vs raw beans/grains and tell me which ones you have more problems digesting.
> - Humans naturally didn't eat the amounts of meat which we consume today
Humans "naturally" ate whatever was available and edible, in northernly latitude they certainly ate ridiculous amounts of meat what with most of the food available outside of high summer being hunted or fished. Humans are not a vegetarian species, and their survival on a strictly vegetarian diet is non-trivial.
Furthermore, our staple cereal carbs literally didn't exist in the "natural" diet timespan, the sources of carbs would have been fruits (where and when available at all) and fibrous and starchy tubers, so your appeal to nature isn't exactly helpful to feeding the world while solving climate change.
Finally:
1. not all meats are equal, poultry has an FCR of about 2 (that is 2 units of feed will produce 1 unit of chicken or eggs), rabbits and pigs are around 3.5~4 and beef cattle is ~6.
2. of note, dairy is worse than beef on an FCR basis.
3. OTOH not all feed are equal and I don't know that FCR takes this in account (cattle being fed raw roughage while poultry or fish is fed concentrate)
4. feed can be a side-product of other food production (e.g. straws) or it might be produced on lands otherwise inclement to human food production, or as part of a rotation scheme