“Good and bad are determined by what adds or subtracts to human flourishing.” This is a common retort for those who want to hold that moral values and duties are more that subjective and yet remain natural. If this was the case then morality would be objective as a standard that transcends personal feelings and opinion is provided. The kernel of truth here is that much of morality is for the purpose of preserving the dignity, welfare and richness of human life. However, I submit this foundation is inadequate for the following four reasons.
First, moral truths carry normativeness, that is, they provide a standard that prescribes what “ought” and “ought not” to be. Human flourishing is merely descriptive of what “is” and “is not.” As something that only describes nature, there is no prescription of what ought or ought not to be that arises, and therefore whatever follows does not fit the description of what we know morality is like.
Second, the reduction of a moral property to a natural property is always ultimately unsuccessful. In this case, in order that we might weigh what was right and wrong we have to define how we measure human flourishing. Say for instance we concluded that human flourishing is measured by an increase in the population of the upper class. That would mean that taxing wealthy people at a higher percentage of their income, purely on the basis that they refuse to have large families was right and good. But that doesn’t fit, because that is discriminatory and immoral, but according to the reduction of the moral property to a natural property it was “good” because it would be promoting human flourishing. Further, on this same reduction, forcibly distributing the many children of a lower-class family into many different upper-class family homes to be raised as servants with free food, clothes, warm house, and education would be a so-called “good” because such action promoted human flourishing, but this is also immoral – it is splitting up families to enforce servitude. One can always find immoral and repugnant examples when moral properties are reduced to natural properties, such as human flourishing.
Third, if right and wrong are determined by human flourishing this succumbs to the temptation of speci-ism. Speci-ism is an unjustified bias for ones own species. But what is there to make the human species anything special? One has to justify that position with reasons, and naturalism is inept at doing so. It just asserts it. Why is Richard Dawkins is wrong when he says,
“There is at bottom no design, no purpose, no evil, no good, nothing but pointless indifference . . . We are machines for propagating DNA . . . It is every living object’s sole reason for being”?
Tell us why the human animal is endowed with special privileges, inherent worth or dignity? Only then can one declare that human flourishing is the determinative factor for what is right and wrong. If naturalism is true then there is nothing really wrong with a man forcible copulating with a woman, for this occurs all the time in nature. Christianity however provides an excellent reason why rape is wrong. It is wrong because it is a violation of something sacred – but how can it be sacred if it is mere matter?
Finally, who determines what human flourishing means? Is it the capitalist or the Marxist? Is it the victim of HIV, or the person who wants to dispose of all HIV sufferers? Certain socio-political movements that have equated good morals with that which promotes human flourishing include Communism, Eugenics, and even Nazi Germany. This is not to impugn the ethical theory with guilt by association. It is to point out that there are radically different ideas on what human flourishing entails. The Nazis, for instance, believed that the extermination and destruction of all Jews, homosexuals, people with black skin, intellectually handy-capped, the infirm, dissenting Christians, and all enemy troops was for the benefit of humanity as a whole. But what is there qualitatively that sets our idea – that this is not an acceptable moral belief – above the moral beliefs of the Nazi’s?
Our moral indignation towards different counter-perspectives provides a powerful reason to think that something else other than human flourishing – though a noble goal – is not the paradigm of goodness. If there is one thing we know when it comes to morality, it is that Hitler and his cronies were objectively wrong. Condemnation of his evil regime is right and good. But from their point of view they were only acting towards the goal of human flourishing, and the brief pain and suffering they wrought in the present was acceptable when compared to the utopia they were helping to ushering in. When we say they were wrong and believe we said something true then we make a value judgment that contradicts the Nazi value judgment, it strongly suggests that there is something else other than human flourishing that adjudicates that judgment. For you cannot found a foundational value judgment with another value judgment.
In summary, human flourishing is not an adequate ground for the objective moral values and duties we clearly perceive. First, moral truths are prescriptive norms and human flourishing does not prescribe what ought and ought not to be, it only describes what is and is not. Second, the reduction of the moral property to a natural property is unsuccessful. Third, it succumbs to the temptation of speci-ism – an unjustified bias for ones own species. Fourth, there is no qualitative way to distinguish different interpretations on what human flourishing entails, and our moral intuitions tell us there obviously is a qualitative difference suggesting that human flourishing is not foundational after all. Therefore, human flourishing is not an adequate foundation to build an ethical theory on.
 This reason for the wrongness of rape would be consistent with a divine command theory of ethics, as breaking God’s command would constitute a violation of something sacred.