Heebie I think it's very important not to lump chronic illnesses under the psychogenic umbrella. It's a connection that people with chronic conditions have long fought against, and the idea that if you can't find a physical reason for X then it must be caused by X is very outdated. Just look at the whole idea medicine used to have about stomach ulcers being caused by stress - now we know that they actually come about by bacteria.
If fibro is possibly a catch-all diagnosis, then CFS definitely is. King's College London is currently researching into the cause of CFS and has received complaints to the GMC about their research into the link between CFS and mental illness. This might sound drastic, and you're right that mental illnesses are not 'lesser', but you can understand the complainant's point(s) if you experience the 'treatment' for CFS yourself, which is based on outdated NICE guidelines from a now redundant study under the misguided view that there is no physical explanation thus far, so the disease MUST be MH in origin.
If you can't prove the origin of the disease, why would you spend time assuming that it must be MH related and therefore you should treat the patient for making themselves ill?
No, we know that MH patients do not make themselves sick. But this what people with CFS/fibro are constantly told they are doing if they take up 'treatment', because it is neither truly regarded as MH nor as physical. It's barbaric, dehumanising, and fucking distressing to go through.
There is no problem or fault with having an illnesses rooted in MH, of course not. But the reason chronic illnesses sufferers are so keen to widen that particular gap is precisely because we don't know where these illnesses do originate from. These issues are again all compounded by them being catch all diagnoses, because a percentage of sufferers probably do have some MH issues thus clouding up the issue further.
It's one big fucking medical mess.