While that is indeed a logical fallacy, doctors are in the business of evidence-based care. How could a doctor responsibly recommend a course of treatment for something which has little evidence, as something unproven would have. Many treatments have both positive and negative effects, and a doctor would typically only recommend a treatment when the good outweighs the bad. On the flip side, there many unproven or proven ineffective treatments patients frequently self-prescribe/self-administer which a doctor would let slide on the basis of it also being harmless. After all, the placebo effect is powerful in and of itself. Taking a wholistic view, medicine is about maximizing the quality of life for patients, as opposed to just being about curing everything. It’s not clear to me how a doctor could responsibly recommend any treatment with potential downsides to a patient with an unproven diagnosis. Such a treatment might indeed help the patient, but it’s a risk/reward tradeoff that needs to be balanced, and while the patient should absolutely be involved in deciding where to draw the line, the vast majority are simply not knowledgeable enough to accurately assess the situation.