Or keep to traditionally held beliefs even after without ever considering that it could be wrong.
You're the one expressing the idea that we understand enough about the complexities of the human body to make definitive pronouncements even though scientific experts in numerous fields acknowledge that we don't really understand many of the workings of the human body.
We don't even really understand something as well studied as cholesterol, yet you are highly confident we understand the complex, dynamic interactions of countless aspects of human biology as impacted by something as fundamental as diet.
Humans: We have been consistently wrong in pronouncements regarding this complex system that we still don't really understand.
Also humans: This time we've cracked it! There's no chance we are wrong this time. Anyone who says otherwise is anti-progress!
No there isn't. Not the least which because opportunistic carnivory exists even in obligate herbivores under specific circumstances. But, again, that's not how evolution works. We didn't evolve to eat meat any more than we did not evolve to eat legumes just because our ancestors did not have access to them. What was and wasn't available doesn't translate to what was the most efficient, nutritious diet possible.
Why are you so certain about this when scientists are not?
Meat and Nicotinamide: A Causal Role in Human Evolution, History, and Demographics
Better diet with more meat/nicotinamide closer to our evolutionary norm helps cognition... Being in denial about our need for animal products and not accepting that ‘meat hunger’ is biological and not a matter of taste, or cultural history, or perversity, or to signal status/wealth/masculinity or our war-like nature does not help.
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Human adaptations to meat eating
This may point to significant meat ingestion as part of an omnivorous diet already in robust australopithecines and early Homo. Therefore we may postulate that physiological, anatomical and behavioural adaptations to habitual reliance on meat eating occurred in the hominid lineage at the australopithecine stage.
Human adaptations to meat eating