Thank you for pointing this out! I glossed over it in the title, but it is bears special attention to avoid falling into any traps of rhetoric.

There definitely seems to be a trend in diet right now to search for the "natural" cure to all our ills. The Paleolitic Diet is probably the best example of this because it is explicitly named as being based on the past. There is an unfounded belief that primitive people were healthier, stronger and better in many ways. However, I don't know of any evidence to support those claims and most of the arguments don't hold together if you don't assume the correlation of natural and good.

I'm really curious what causes such as fixation in our modern culture on the "natural" as being healthy and good.

There's also an odd opposite assumption that anything that is "unnatural" is probably "bad". GMOs are a good example of this. Anything derived through selective breeding is good, but as soon as you directly modify the genes it's bad, despite more rigorous testing.