A sedentary population can't have too much fat and sugar without becoming very fat. Basically the situation we have now ...
You either believe calories are calories (in which case, while fat has about twice the number as carbs and proteins, it is still the number of calories you consume that matters for weight maintenance) OR you believe that a low carb diet, which can be quite high in fat can maintain a good weight. Either way, fat is not the enemy, it’s simply one component of a normal human diet.