Sorry to make a little diversion from the subject but, speaking of the BPS belief ...
Last week I had a conversation with the syndic of the Order of Psychologists in my Province (CA). I wanted to know the exact limit on the field of competence of their members. I asked him 2 specific questions.
The first one : can a psychologist claim that psychotherapy
can cure a physical illness? He clearly replied
no and that if I witnessed such an assertion from a member, I had to report it to the syndic of the Order (which I already knew). (The syndic deals with complaints from the public concerning a member and decides, after investigation, whether this complaint should be brought to the disciplinary committee of the Order, in accordance with the professional code and ethics.)
The second one, and this was where the going got tough: can a psychologist claim that psychotherapy
can reduce symptoms of physical illness? He answered
yes... Oh Lord ... I then asked him what evidence he was basing himself on to say this, arguing that to my humble knowledge no evidence of cause and effect really existed, at least for the majority. There, it seemed to me to search for his words for a few seconds. He then explained to me that psychotherapy could "reduce the impact of stress on illness " and ended up referring to Hans Selye *, the father of the concept of stress. With each additional question I asked him to question his assertion, he kept repeating the same sentence to me "psychotherapy can reduce
the impact of stress on the disease ". I then said to him, "Maybe psychotherapy can reduce stress through relaxation or help the person cope with the disease, however, how can you be sure that stress can reduce the extent of cancer, for example? See, I think you keep repeating that same very general sentence to me because
the direct cause-and-effect connection is not proven. There he whispered a little "yes" !! (that it was true.)
Although I remained calm and cordial throughout the conversation, I believe he was glad that I ended the call.
*
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5915631/