Yes, my experience with CBT very much leads me to believe that shame is a highly destructive emotion, more likely to cause someone to withdraw and disengage from life than to promote lasting positive change in behavior.
But no emotion is inherently destructive. We should feel shame at certain things. If you tripped an old lady and didn’t feel shame, I’d say you were a psychopath, or if you simply threatened to kill anyone who you didn’t like.
It’s also notable that absence of shame is characteristic of psychopathy, and even Buddhist psychology states that an absence of shame is an impediment to enlightenment.
I completely support the idea that excessive or inappropriate shame is a major part of many if not most psychological disorders. Nothing supports the idea that all shame is destructive.
On the topic of obesity, I do agree that shame is unlikely to help. In fact I suspect that shame is more likely to be part of the cause.
For a behaviour trait to exist in species far from each other in the evolutionary tree suggests there is a real survival benefit to having it.
Doesn't mean it is beneficial in all cases, or that it doesn't feel shit though!