There is no obligation on the city to protect citizens from their own choices. Citizens are responsible for their own bodies including what they eat and drink. Making any part of government responsible for this would mean a need for much more regulation on almost anything that would protect lives. In this case it would require a much tougher response than simply a partial ban that only affects large drinks. Moreover if there is such an obligation why is it the obligation of the city while the state does not have such an obligation with regards to 7-11s?