I have read the Weston Price concepts and i understand what you mean, maybe some people have a strong immune system which can destroy parasitic worms.
Maybe that's true, or maybe they have never been infected as much as we are.
The fact that we eat foods from all over the world, the fact that people travel all over the world, the fact that people have sex with people of others ethnicity (and so others parasitic infection), the fact that when you eat in a restaurant your food may be prepared by a human which has lived or traveled in another country, the fact that our water supply is connected like a network, the fact that our waste is connected in a network and pets may go play in it and then come in our homes.
All these are vectors of infection that maybe were not present in primitive people lives. At least they were only infected by the local infection and so their immune system maybe has the time to become stronger.
Let's say we agree with weston price theories, that when people eat primitive foods and live with "natural" habits then they have a strong immune system and health.
What Weston Price doesn't explain in his book is that the human females of the tribe may have had many babies and childs who have died because their immune system were not strong enough.
So let's say i was born with a weak immune system, do i have to die because of these parasitic worms infecting me ? Or should i fight back and kill them with herbs ?
The natural selection theory is of no use for me. I hope you understand. Maybe my immune system is weaker than others, but i want to do all i can to get rid of these parasitic worms and keep great health and energy. And if i have to clean my digestive tube and flood it with herbs from time to time, i'll do it.
Now to make you think about Weston Price theories, read about Columbus story when he went to the caribbean and south america. According to the theories of weston price (who probably wasn't aware of the existence of parasitic worms in his time) primitive people of america should have kept great health because of their "natural" habits and primitive foods. That's not what is explained by the ancients : (a random link but you can find others which explain the same thing)
Disease: western hemisphere peoples not exposed to many infectious diseases that were in Europe; within 100 years after 1492 thousands of peoples had died because of measles, mumps, typhus, diphtheria, smallpox. Europeans say that it was "divine intervention". today AIDS/HIV similar to the problems that Native Americans faced as they tried to cope with and eradicate the disease... but they did not have the benefit of modern medicine