Yes, there may be a good reason why we don't produce broad band antibiotics in our gut as well but this does not prove the point you made. We have all kinds of illnesses and nature clearly failed to support us with means to fight these illnesses. The fact that infected cells die may be very problematic, maybe it even prevents those who are most ill, from taking it. On the other side, as I said, nature is very simple, it doesn't care if we die. In the end you can choose by yourself if you want to buy "bad" drugs from pharma companies or not. But it doesn't look like nature has cured CFS yet.