Christopher Hitchens, author of "God is not Great", asks this question: "What moral statement can Christians make that atheists can't?" Since most of his attacks on Christianity revolve around moral judgments of the Christian God and His followers, it seems to be a cornerstone of his atheistic faith.
The answer really, is quite easy, if not simple. For if we are to answer the question directly, then the answer is "None". There are no moral statements that Christians can make that atheists cannot. But before the non-believers break out the champagne and declare themselves the winners with Hitchens as the conquerer-in-chief, let's take it a step or two further. Because if the question is taken to mean "What moral statement can Christians make that atheists can't, and provide a logical, reasoned basis for making those moral statements?" then the answer is "All of them."
Now to be sure, there are a bunch of theories that attempt to explain morality. Some of them, from the noncognitivist side, deny that moral statements are indicative at all, i.e. that they have ontological meaning, and that they are either true or false. Moral statements are reduced to emotion or moral commands (if you love it, do it!).
On the congnitivist side, the subjectivists say that moral statements are really just statements about the one who is making the moral statement, i.e. the subject. That can extend into societies, where it may be a sociological statement to say that "our culture dislikes rape". The problem here is that this is not a normative statement.
The objectivists agree that moral statements are true or false statements of fact. This group can be further divided into ethical naturalists and ethical non-naturalists. Their disagreement arises around whether moral properties can be reduced to and identified with non-moral properties. By its nature, ethical naturalism is a reductionist theory which attempts to define or reduce ethical terms to physical natural properties, that are biological, sociological, psychological or even physical in nature. In my estimation, this is where Hitchens has to reside. He makes absolute moral statements about God, so he cannot be non-cognitivist, and neither can he be subjectivist.
So as a natural ethicist, his moral basis has to reside inside one of these frameworks that describe "right" from "wrong": 1. What is approved by most people, 2. what most people desire, 3. what is approved by an impartial observer, 4. what does the most good for most people, 5. what is best for human survival, 6. what is in the maximum interest of all people etc.
The noteworthy observation about this framework is that it is not morally irreducible, it is reducible to to the properties mentioned above. Science can then assign values to these properties, and it can be measured.
But how does ethical naturalism stand up to its own standards? Can we make statements about ethical naturalism that hold true, and are non-circular? Can we say that ethical naturalism is morally right, without first accepting ethical naturalism as the theory by which it should be judged as right or wrong? Of course not, it is absurd and viciously circular. That is because the ethical naturalist confuses "is" with "ought". Every moral statement carries with it a normative "how we ought to behave to be morally right". If an act is right, then one ought to do it. But here is the problem, physical properties, like the ones the ethical naturalist attempts to reduce moral acts to, carry no normativeness. They are simply natural properties that exist, regardless of how we ought to behave.
Secondly, the reduction of morality to the framework described above fails, because the reduction simply does not work. The majority may be wrong, such a thing as an impartial observer does not exist, and the most good for the most people depends on who is making the moral statement to begin with, i.e. who decides what is the most good for the most people.
Furthermore, ethical naturalism faces the problem of a personal internal infinite regress, since naturalism is wholly dependent on the senses to interact with the environment in which we live. But how would you then know that what you are doing is right or wrong? How do you "sense" it? And how do you know that that sensation of knowing that your act is right or wrong, is right or wrong? Do you "sense" that? How about that sensation? how do you know that your sensing of your sensing that your act is right or wrong, is right or wrong? And so it will continue, to the point of an infinite regress, and one may never know that what you are doing is right or wrong, when one starts the regress by reducing morality to physical properties and measurable sensations.
So while Hitchens may ask the question, and even receive an initial answer that satisfies him and his followers, the deeper investigation does not work for him, at all. He is firmly entrenched in fatal relativism and cannot escape infinite reduction.
Christians believe that humans are created in the image of God, and therefore have God's moral will to guide them. Even if atheists deny this, they cannot escape it. Even if they use this built-in morality to assault God and Christianity, they cannot do so without using that morality. I once heard it said that it is like a child slapping his father in the face while the father was carrying him across an alligator-infested swamp. An apt analogy, I think.
Morality is based not only on the will of God, but on His very nature. And since we all share a part of His nature, we are moral. Thanks be to God.