For some reason people who never experienced primitivism wax romantic in their celebration of primitivism yet ignore the fact that as soon as you give a primitive a match, he no longer wants to rub sticks together to make his fire.
I agree but there is some merit to this diet. The idea is to only eat the natural things that humans ate and adapted to for tens of thousands of years rather than eat man-made items that have only been around for a few hundred at most. Some of the chemicals and processes used in food today have only been around for years or decades.
I never did a full diet like this but at one time I ate only organic for several years. I even used organic soaps and filtered my water. I felt much better, never had headaches, my skin looked much better and I lost 100lbs without feeling hungry or working out more.
Everyone is different and we have no clue how all these toxins, chemicals, hormones, etc affect each person. Unless you have a disease that requires medication, one should consume as little man-made chemicals as possible.