If I understand William Craig’s third objection to AMR, then he is basically offering an inductive teleological argument for the existence of God (similar to how Richard Swinburne argues for God) based on the assumption that there are objective moral values plus the claim that humans and the circumstances in which humans find themselves are such as to allow humans to live morally significant lives (we have free will, are able to grasp moral principles, are able to reason from moral principles to specific moral judgments, we have some tendency to behave in accordance with morality, and also face temptations to behave contrary to moral duties, and we have lots of opportunities to make morally significant choices that impact the lives of others).
Craig also needs to claim that not only is this correspondence between objective moral values and the nature of human life to be expected on theism, but that it is “fantastically improbable” from an atheistic or naturalist point of view.
If morality is a purely subjective thing, then God does not exist. At least, God as conceived of by most theists does not exist. The word ‘God’ as used by most theists entails ‘a perfectly morally good person’. If there are no objective moral values, then there is no such thing as a person who is ‘a perfectly morally good person’. That is to say, sentences of the form “So-and-so is a perfectly morally good person” are neither true nor false. Since no such statement is true of any person, no person could be objectively identified as being a perfectly morally good person, and thus no person could be objetively identified as being ‘God’.
Of course, even if morality was purely subjective, there could still be an eternal, omnipotent, omniscient person who created the universe. But if there were such a person, we could never conclude that this person was a perfectly morally good person.
Since we could not conclude that any person was perfectly morally good, we also could not conclude that any person is worthy of worship. An all-powerful and all-knowing creator would simply be a interesting and unusual person, but there would be no compelling reason to worship this person. If there is no person who is perfectly good, then there is no person who is worthy of worship, and no person worthy of the title ‘God’, in the sense that most theists intend.
What if morality is objective? What if there were “objective moral values”? Craig’s implied teleological argument assumes that there are such values, and also that it is “fantastically improbable” that the random natural process of evolution would lead to the origin of human creatures who were capable of living morally significant lives. Why would random natural processes have any tendency or inclination to favor the existence of such creatures?
If moral principles and moral virtues serve the purpose of helping humans to thrive, then it might well be the case that moral principles and moral virtues also help humans to survive and to pass on their DNA. In other words, if the purpose of morality is to help humans thrive, then morality might well have survival value.
According to Jesus, the Sabbath was made for man, not man for the Sabbath. In other words, the rule (one of the Ten Commandments) to take a day off from work each week serves the purpose of helping people to thrive (to be happy, healthy, cooperative, and successful). It is the benefits to human beings that justifies having such a rule. If, on the other hand, following this rule was harmful to humans or made human life miserable, then there would be no good reason to have or to follow such a rule.
In the debate between William Craig and Richard Taylor, Taylor makes some comments along such lines in his opening statement:
You don’t have to be religious to realize that for human beings to live in peace and happiness, they must not assault each other. I may want to assault, but I do not want to be assaulted. If I’m tempted to theft, still I do not want to be stolen from. If I’m tempted to murder, I do not want to be murdered. The rule thus emerges: Let no one do these things. Then we can live in peace. Then we can realize the human goods we need. Now if anyone thinks that we wouldn’t know that if God had not come down and given these laws to Moses on Mount Sinai, if anyone thinks we wouldn’t know that otherwise, that person must believe in the tooth fairy.
The natural basis of ethics is human need. There are certain things which all of us hate. We hate to bleed, we hate to be wounded, we hate to be killed, we hate to be stolen from, and we make our laws according to this. The natural basis is certain universal needs: the need for security, for safety, for love, the need to bring up our families in security, to teach our children to fulfill our own potentials as we can, and having these needs, we have rules. We have rules, and they are important.
(Craig–Taylor Debate: Is the Basis for Morality Natural or Supernatural?
If Taylor is correct that morality serves the basic needs of human beings for security, safety, and for love, then morality appears to have survival value, and Craig’s claim that it is “fantastically improbable” that the natural process of evolution would have a tendency to favor the origin of moral creatures (of creatures capable of living morally significant lives) is false. If morality has survival value, then it is NOT highly improbable that evolution would produce creatures who have characteristics that correspond with “objective moral values”.
However, Taylor’s view is that morality is conventional. Morality is something that human beings came up with in order to serve various basic human needs (for security, safety, love, etc.). If morality is something that human beings made or invented, then this would explain why morality has the PURPOSE of helping humans to thrive or to obtain basic human needs.
On the other hand, if “objective moral values” exist as necessary truths or as abstract entities like numbers, then it is unclear why “objective moral values” would have any tendency to serve basic human needs or to serve the purpose of helping humans to thrive, to be happy, healthy, safe, secure, and successful. So, Craig, or other defenders of Christianity could still press a similar point: it is fantastically improbable that such “objective moral values” would just happen to serve the purpose of helping humans to thrive.