The problem is, in part, that there is definitional blurring here, and the psychogenic brigade is blurring the lines a lot.
I think we need to start with something like "every expert agrees that people with CFS are really suffering". Then maybe "CFS is such a broad diagnostic category that misdiagnosis might be on the order of 40% even if the doctor is careful, at least if they use the general CFS criteria". Then "however if you use ME criteria the misdiagnosis rate goes way down, and you can objectively measure most of the major symptoms". Point out that while CFS definitions may only be accurate, somewhat, less than 60% of the time, ME definitions using cutting edge technology seem to be accurate to 95% of the time.
The problem is the diagnostic category of CFS is invalid. Doctors mostly kind of get that I think. Some then go on to conflate the diagnostic category, which like many diagnoses is man-made, with the disease the patients have. Its more about diagnostic accuracy, but some take that too far and go into denial mode.
However as I pointed out in a recent blog, if you go from "this category is invalid" to "this disease does not exist", its such a leap of logic that if you believe it then you have to throw the DSM in the bin, as none of those are real either. Its a fallacy. Real disease, mislabelled, is still real disease. The people still deserve respect and care, its just the category that needs to be treated as speculative.