That’s a senseless statement. Nobody lives in the Stone Age today. That’s a period of time.
If you’re referring to primitive tribes with no outside world contact, then you’ll need to provide evidence and definitions for healthier/happier. They have high infant mortality rates, they kill disabled children, they die from treatable illnesses, and they starve during bad years.
Of course they have mental illness, there is no evidence they are immune to Down syndrome, schizophrenia, or anything else. They are just much more likely to murder or ostracize people having too much difficulty fitting into the tribe.
>It is harmful, we consume it in vast quantities
Ugh, you accidentally forgot to provide any evidence of its harm again. You just preceded it with another naturalistic fallacy that implied that it must be harmful because it’s industrial.