Trans fats are unhealthy, with an abundance of scientific evidence to that effect. Friedman would probably not have opposed banning them in most applications as he saw a role for the State in setting the "rules of the game," with public health a recognized basis for action.
Assuming you are a conservative since you are here, do you really believe regulating trans fat is within the purview of a city government?
Saturated fats and carbohydrates can also be unhealthy. Shouldn't they be banned too? As a matter of fact, most foods can be bad for you if they are overconsumed. If you overcook bacon, powerful carcinogens are formed. If you under-cook burgers you're at risk for e coli. Should the state force the food industry not to make crispy bacon if a customer wants it? Should we be forced to eat burgers that are only cooked well done? There is solid scientific evidence to back all of this up. We could save lives. Where does your doo gooding end?
When it comes to food, the state could regulate just about everything consumable for our own good. That might help impact the obesity epidemic. Or, they could leave us the hell alone instead of making decisions based on ignorance and highly questionable scientific evidence.