My one question to mill would be that why is it that the effect of an action on people having overall happiness or not could be the sole factor that decides if that action is moral or not. For example your in some different country and you happen to save a random man’s life you saw in trouble. That man happens to be one of the most hated/wanted people in that country and he was better off being left for dead. In that country you might cause overall unhappiness but once you are back home in your own country it is looked at as a moral deed or action that you did overseas. In that situation it is simply a matter of different culture/society which determines over happiness of people and i do not think that should be the sole reason for defining an action as moral or not.
I think that mill would respond somehow by saying that the overall happiness of that country does not matter in the “bigger” scale. Where everyone in the world would be happy because you saved a life. Im not too sure what he would think of this situation but i think he would believe that every action no matter where has some kind of moral value and once again depending on overall happiness of the people no matter what country or type of society.