Thanks for your detailed reply. I don't quite think that you've addressed the core of my point, though.
In your description of the patients' symptoms, you already make a strong link between the symptom (patient reports blindness, patient reports inability to feel legs) and a pathophysiology that you currently believe to be true, namely that the "patient truly believes that they have this symptom".
I see no reason to make this link. At the moment, I would classify your viewpoint as a mere belief: You believe that the main etiology is the patient's belief. But do you have evidence for that etiology?
On the question of evidence, you state that there are several models, but also that
Because there are multiple models for this disease, its obvious that we don't yet fully understand it.
The problem is: I don't see that these models are scientifically validated in any way. But science is the only way to distinguish personal belief from "objective reality". Here are a few problems:
As far as I understood, neither of the models that you mention have experimental evidence. Can you cite an experiment that measures an "internal unconscious conflict" and demonstrates that this is converted into symptoms? Or is there a measurement of the fear response in the amygdala and a demonstration that this manifests a symptom?
Diagnosis of exclusion is logically unsound. You perform some measurements (blood tests, neurological tests,...) today and find no pathological results. But what if a new method of measurement is discovered tomorrow that would show a pathological result? How do you exclude that possibility? The only thing you can state with a degree of certainty is that the patient has none of the currently known neurological diseases, but not that he has no neurological disease.
Note that this is not a theoretical problem. One prominent example is the discovery of Helicobacter pylori: "In 1982, [..], stress and lifestyle were considered the major causes of peptic ulcer disease". It was believed that peptic uclers were caused by stress, but this belief was overturned by a new method of measurement: Direct observation of Helicobacter pylori (and subsequent experimental confirmation that it is causative for the disease).
Alternative explanations. This is similar to the previous point, but adds concrete counterproposals.
Here is a story that is similar to the paralyzed leg, but clearly has a different pathophysiology. After taking pain medication, I can touch a hot oven without feeling pain. However, I will still instinctively withdraw my hand. Apparently, it's a separate reflex (and a repeatable experiment). Likewise, it is conceivable that the patient is genuinely unable to feel his leg (and not just believing that he can't), but the reflex of withdrawing still works.
Now, I'm /not/ claiming that this is true -- it could be false -- but there needs to be an experiment that distinguishes between those possible explanations. Otherwise, the evidence in favor of one possibility works equally for the other one.
On another note, if I understand you correctly, you seem to want to argue that some patients are 'insta-cured' if they believe it, so this means that the patients that don't believe it could benefit. I'd like to point out that this is logically unsound -- this cure has only ever been observed in patients that believe you, but this doesn't give any information about those that don't. It could very well be that they don't believe it because their symptoms did not resolve, even if they tried to believe it.
In the end, my point is again:
At the moment, I see no scientifically sound reason to classify the proposed pathophysiology of F44.5 as anything other than "belief".
In that light, disallowing patients (or anyone else) from challenging the proposed pathophysiology, because that very action reinforces belief 1, is unherently unsound.