If morality is truly objective, how does one measure it? Remember, something objective is something that does not arbitrarily change based upon the perceptions and interpretations of observers; it is something factually true for all of reality. So again,…
1. I’m not sure that poses a major problem to this argument. Lets say that everyone had a desire for ice cream, would the fact that the specific ice creams they wanted were different make the ice cream acquiring strategy significantly different for society? It might change the logistics of the situation, but by and large it would not change what needs to be done.
2. This sort of reasoning is called a hypothetical imperative. I’m not sure how I would respond to someone who didn’t think we should act in a manner that is most likely to achieve a specific goal. Whatever system they adhered to which told them that would not be a rational one, whatever it is.
It’d be like a student responding to a professor’s advice that “if you want to do get a degree l, you should study” with “I deny any rational connection between the acts of studying and getting a degree.” It’s true that the two aren’t necessarily connected, but studying is generally the best strategy of achieving the goal of a degree.
3. I think the fact that people want these things only for certain people weakens but does not eliminate this form of morality. No one can achieve happiness and health in a vacuum. If I want persons A, B and C to be happy and health and you want persons D, E and F to be happy and healthy, we both still need a societal network in order to make all that possible. At the very least, society needs to be able to produce doctors, food, drinkable water, entertainment, etc.
If I act in a way that destroys this societal network, I am only indirectly hurting A, B and C’s chances of being happy and health, so it makes sense for me to behave in pro-social (i.e. moral) ways.
4. The objectiveness comes from what morality actually is. On my view, morality is a “science” for discovering those actions most likely to satisfy the desire for happiness and health that humans have. It is objective in the same way that medicine is. Medicine tells you the objectively best ways to achieve health, regardless of whether you personally value health or not. Morality tells you the objectively best ways to achieve happiness and health, regardless of whether you personally value happiness and health or not.