All that follows is from commenter RDM:
Perhaps the greatest irony of this whole discussion, given that it is primarily dealing with materialists and their objections to self-evident moral truths, is two-fold.
First, consider that in many respects, philosophical arguments are simply plausibility comparisons. One argument/view is simply more plausible than another. Now, in terms of a plausibility comparison between “it is always and everywhere wrong and evil to torture a child for fun” and “materialism is true and thus it is not always wrong to torture a child for fun”, the former is light-years more plausible and certain than the latter. Any worldview that rejects that moral truth is infinitely less plausible than the moral truth itself. In fact, that moral truth is more plausible than the claim that “matter itself exists”. And so, the irony here is the following: the moment that I doubt the truth of that moral statement is the moment that I gain infinitely more reason to doubt the truth of materialism (or naturalism, to use a different name for it).
Now the second great irony in hearing the materialist argue, in part, against self-evident truths, is that materialism, at its core, depends, in a certain way, on the idea of self-evidence. And not in the ways already mentioned—although in those as well—but rather in that the existence of matter itself is arguably supported by nothing but self-evidence. After all, what is the materialist’s proof or empirical evidence that matter actually exists? As Berkeley and others showed, not only is there nothing that can “prove” that matter exists, but there are actual good arguments against the existence of matter. And so, for the existence of matter, the materialist can offer, as inferential evidence or proof, nothing more than the person who says that “it is always wrong to torture a child for fun” can offer for his view. And remember, the burden of proof is on the materialist, for he asserts the existence of matter. And so, if you think yourself justified to rejecting the aforementioned moral claim, than you are doubly justified in rejecting the very existence of matter, and, in turn, in rejecting materialism. So, in rejecting the very moral claim that it must reject in order to be coherent, materialism simultaneously provides us with the very grounds to deny the existence of matter, and thus to deny materialism itself. Materialism, in essence, loses no matter which way it turns.