Let's get this out of the way now, because someone is going to say it eventually. I am a monster. This is not due to any horrible crime or hidden shame. I have no unnatural appetites that need to be sated. Sadly, I am a monster because I accept the possibility that morals are subjective. That concept, that subjective morality is so horrendous that we should deny even its possibility, is the essential thrust behind the Moral Argument for God, one of the five arguments William Lane Craig presents in his paper.
Craig spends comparatively little time defending his argument, instead electing to lay out definitions and bring up related dilemmas. The definitions provide him an excellent opportunity to lobby for the rejection of subjective morals and he does not let it go to waste. Since the end of the Second World War, Nazism has been excellent political capital. If one is able to link their opposition to Nazis, not matter how flimsily, the distaste most people feel towards the actions of Nazi Germany makes it unnecessary to address the actual issues. In making the distinction between objective and subjective morals, Craig tries to link subjectivity to believing that the Nazis were right. Having done that, he feels the matter settled.
I am going to cast things in a different light. The reason this Nazi ploy works is because people feel disgusted by the atrocities committed under Nazi ideology. To put it a different way, people are rejecting the actions of the Nazis based on the emotional reactions they evoke. The problem here is that emotional decisions are subjective ones, so Craig is using subjective moral judgments to garner agreement with the concept of objective morality.
Let me go through this again, because the concept is important. Craig says that objective statements are independent of people's opinions whereas subjective statements are dependent on opinions. (He perhaps intentionally leaves off emotions, but this is trivial since we can see that opinions are the product of emotion.)
The statement "2+2=4" is an objective one, the statement "Apples are the best fruit" is subjective. No matter what we feel about the first statement, it is true, but the second statement relies on our emotional attachment to the glorious apple. By the same token, saying that the Nazi regime killed many people is objective, saying that it was wrong because it makes you feel icky is subjective.
And here we come to the crux of the problem. Moral statements involve emotional content. Few people say this or that is moral because the facts support it, they say that something is moral because they feel it is right. It is my opinion, and you're welcome to correct me on this, that there can be no such thing as an objective moral statement. Moral statements are, by their nature, subjective. To speak of objective morality is nonsense and question-begging.
Because Craig believes he has successfully lobbied for the denial of subjective morals, he makes no attempts to defend his argument. As such, he misses the flaws in his first premise. In the first case, he does not address the possible alternatives sources of objective morality that other non-believers have suggested. In the second, it doesn't consider that god might exist and yet morals might still be subjective. (If god decides what is moral, then are morals subjective because they are based on gods opinion?) Either of these, along with the issue I raised above, is enough to make the argument questionable.
Craig does bring up a common problem associate with god and morality, if only to tell us that it is weak. Euthyphro's Dilemma asks which statement is correct, 'God wills something because it is good' or 'something is good because god wills it.' If the first is true, then good and bad are independent of god, if the second is true, they are arbitrary.
Craig's response to this dilemma is to present a third alternative: 'God wills something because he is good.' Unfortunately, examining his explanation of this statement shows it to be nothing more than a repackaging of the second option. Craig explicitly states that God's nature is the standard for goodness, which implies that whatever god's nature might be, it determines what is good. Were god's nature deceitful, callous, and vindictive, this would be, according to Craig, the standard for good.
To wrap things up here, I'd like to point out something that objective moralists overlook. Believing in the subjectivity of morals does not mean being universally permissive. Regardless of whether or not objective morals exist, human morality is a human social construct that has demonstrably changed over time. If I want my moral values to be those of society as a whole, I cannot allow people to do whatever they please. Likewise, I cannot simply declare by fiat that something is wrong no matter people think. I must persuade people that my moral opinion is the correct one. Ironically, so must Mr Craig. Really then, what is the difference between our moral stance?