This would suggest, that jews who defended themselves against the Nazi Authorities were acting acting unethically, but intuitively we generally agree that jews defending themselves against the nazi authorities were not acting unethically. Therefore it is not always unethical to disobey authority.
Dietitians & nutritionists are specialized in determining what we ought to eat if we wish to be healthy. Your logic here would suggest that it would be unethical to eat unhealthy things because it contradicts people who are specialized in making these sorts of decisions. That is not unethical.