Sigh.
Let us take this angle - assume that obesity is due to lack of self-control and will power and a moral failing of sorts. Pretty much like becoming addicted to narcotics is.
For years the treatment for heroin addiction was being told to stop using the drug. That worked as long as people followed that advice. Some managed to do that, a very few. Some were able to get through detox but most of them quickly relapsed. For the vast majority the drug use persisted causing a great deal of other harms. The advice failed for most because most did not follow it … it was too haaaard. The advice itself worked, just not for most of the people who were addicted.
Then it was discovered that there was a way to allow an addiction to narcotic to persist but to still greatly decrease the harm associated with the drug: substituting methadone for heroin. The addicts did not become free of addiction, but the harms, to themselves and to society were greatly reduced.
Current heroin guidelines generally include a role for methadone fairly early in the process. A physician who subscribes to the belief that the guideline for treating heroin addiction should be telling those so affected to stop and that if they fail to do so, well that’s not their problem, the advice works, are not practicing good medicine.
Likewise, even if you believe that obesity represents a moral failing that was present from childhood on, a belief that the approach should be “just take in fewer calories than you burn”, in the face of the overwhelming poor outcome of that approach, would be an idiot of a physician.