Deontology (some things are morally right and some are morally wrong) is true. Materialism is not compatible with Deontology because it is not compatible with free will. Therefore, materialism is false.Naturalists can attack either of these premises. They can claim that right and wrong are not absolute, but are based on consequences. This view is called (surprisingly) consequentialism. Utilitarianism, for example, is a form of consequentialism. This is probably the better attack, based as it is, on intuitive, religious, presupposition. How can one "prove" either side? My own view is that the consequentialist and utilitarian tracks are subsets of moral thinking, which is properly deontologist. I don't know how I'd prove it, however. There are also those who claim that materialism is compatible with free will. This is called compatiblism. I find this idea downright bizarre, and Layman makes my case here:
...the current trend among materialists is not to deny freedom and morality, but to claim that human freedom is compatible with causal determination. In other words, a given act may be both free and determined at the same time.. An act is free for a person if and only if he performs it because he wants to (all things considered). The phrase "all things considered" is an acknowledgement of the fact that a person may have conflicting desires. I may want to go to a party and to study for an exam. If I can't do both, I will presumably do what I want, "all things considered." Thus, for the compatabilists, 'free' contrasts with 'coerced.' When I am not coerced, but rather perform the act because I want to (all things considered), I act freely. But we must ask: What accounts for the fact that I want to perform a given act, all things considered? On the materialist account, every event is the result of prior states of the physical world together with the operation of natural laws. The way the world is today, right down to the last detail, is a result of the way the world was yesterday. Now, I do not have control of the past. Nor do I have control of which natural laws govern the physical world. It thus appears that I do not have control of my wantings if materialism is true. My wantings are entirely the result of factors over which I have no control.Layman admits there are counterarguments, but he finds them unconvincing. The result as he sees it is that materialism has a "problem of evil" at least as bad as that of conventional theism because it struggles to even admit that it exits. If we are not free, then 'right' and 'wrong' are empty containers and virtually all of us act as contrary to that. Most of us would speak to it too. The point of all this is that the arguments for theism are at least as good as those for materialism, given that this is a case in which the standard is the "preponderance of the evidence" in a comparative case. Both sides ought to see they fall short of a more stringent and fulfilling standard. They can see and account for evidence given by the opposing view. Much, then, depends on the weightings and intuitions over deontology and on how one defines freedom. The fact that naturalism is commonly supposed as the objective, neutral view tells us more about our position in post enlightenment history than it does about true ontology.