I do forget Mars that in our society fat is bad and low carb is a fad are drummed into us...by everyone. Government, vast majority of doctors, American heart association, American diabetes assoc.
So I know very well a Dr. Can mean nothing.
All carbs are not bad. The heart of my diet and Paleo and Primal are non-starchy vegetables.
However. People have carb thresholds. They do differ. People can choose to believe this or not. Go over yours and weight loss will be neigh impossible. And you are putting yourself at risk for diabetes, heart disease, cancer, dementia, arthritis, etc.
For some a couple pieces of fruit a day are fine. For others it would put them in ill health and cause them to gain weight.