I have said in past posts that freedom is important because it gets us what we want and that freedom is incompatible with immoral decisions. It follows quite simply that the importance of freedom means that there must be more than one good thing we can do. Although this is not by itself an overwhelming reason to believe in that particular moral theory, it does contribute to the reasons we already have for believing it.
Remember that freedom is not compatible with wanting to do bad things. So that means that freedom is choosing to do the good things that we want to do. Now suppose that there was only one good thing to possibly do. We speak of such a situation as one in which we are not free. I was forced to stop that criminal, the policeman says. He chose to stop the criminal because it was the only good option available to him. However, without other good options, he wasn’ t really free. Nor is that my only line of evidence. When we discussed the importance of freedom, I mentioned the importance of freedom of choice. That is the sort of freedom that lets us do whatever we want. But what value could that sort of freedom have unless we can choose more than one good thing? I suggest that it would have no value. So at a first look, it appears that freedom requires that there be more than one good option.
As I have suggested, this actual means something for our moral theories. It means that no maximizing theory of morals is true. This is because there is at least one case where one person has a choice in which there are at least two options that are both good. There are two ways to evaluate his choices: the two options are equally good, the two options are differently good. If they are equally good, then there is some measure (preferences, pleasure) that they both equally have. If they are differently good, then there is no measure that can compare them. They are just different and good and that is all that can be said. If freedom is common rather than rare, then it is far more likely that different goods exist than that equal goods exist. But if different goods exist at all, then it is not possible to measure goodness in general. If it is not possible to measure goodness, then it is not possible to get a maximum. Therefore, it is very unlikely that a maximizing theory of morals is true.
If a maximizing theory of morals is false, then it is simply false that we ought to do as much good as possible. Rather, moral theories just tell us not to do bad things. Different goods means that talking about how much good I did is a nonsense claim. It is no different than claiming that blue is more colored than green. Personally, I think that this is acceptable. There is no good reason to believe in maximizing theories of morals anyway. I think that freedom far outweighs any vague moral ideas we might have on that issue.