Could there be a moral argument against moral realism? I’ve been thinking about that question a lot since encountering the work of Melis Erdur. If we consider meta-ethical theses like moral realism to be substantive moral claims which carry potential moral implications, then it seems like a moral argument against moral realism is a real possibility. Admitting this would call into question the (increasingly less) common assumption that meta-ethical theories don’t have moral implications. However, it seems like this assumption is false. For instance, moral realism being true would mean that we have moral reasons to act or refrain from certain actions. That we have moral reasons to act seems like a moral implication. If error theory was true, we wouldn’t have any moral reasons to act, so the truth of realism over error theory would entail moral implications.
If we admit that the boundary between ethics and meta-ethics is fuzzy, then we may have room to think about a moral argument against moral realism. For example, moral realism entails that the moral wrongness of an act is conditional on there being a human-independent moral reality which makes that act wrong (Erdur forthcoming). But is the existence of a human-independent moral reality morally relevant to the wrongness of the act? Is the realist going to admit that if we were to discover that there is no human-independent moral reality, we should drop our commitment to the moral wrongness of a certain class of actions? Remember that we are assessing moral realism, and not whether or not there is an anti-realist theory which lets us admit that an act is wrong even if there is no human-independent moral reality. The realist is going to think that a commitment to realism, and nothing less, is needed to put our moral practices onto secure foundations. So, she probably won’t immediately turn to a form of anti-realism as a form of moral palliative care.
It seems like we have the makings of a moral argument against moral realism. I won’t try to provide anything more than a brief sketch in this post, but I hope to explore this notion in more depth soon. In short, if we eschew a hard and fast distinction between meta-ethics and ethics, there opens up the possibility of considering meta-ethical theories as substantively moral, and as such evaluable by first-order moral standards. For instance, we could assess moral theories by the adequacy conditions provided by Theresa Tobin and Alison Jaggar (Tobin and Jaggar 2013). If moral realism fails to live up to our evaluative standards, then it would constitute a substantive moral mistake (Erdur forthcoming). The same could go for various forms of anti-realism, like expressivism and error theory.
 I am unsure if this question ought to be answered by a survey of self-proclaimed moral realists. I can think of good reasons for and against doing so.
Erdur, Melis (forthcoming). A Moral Argument Against Moral Realism. _Ethical Theory and Moral Practice_:1-12.
Jaggar, Alison M., and Theresa W. Tobin. “Situating Moral Justification: Rethinking the Mission of Moral Epistemology.” Metaphilosophy 44.4 (2013b): 383-408. Web.