As to the name of the fallacy, I'm not sure. I suppose it's something like a misplaced expectation? The mistake is thinking that a certain theoretical moving part should do more work than it is rightly expected to do, while refusing to examine those moving parts which are rightly expected to do that work. EDIT: An example of a similar mistake might be thinking that a decision theory should tell you what to value and why, or that evolution should give an account of bio-genesis.
The SEP article's last section, on deontology and metaethics is very helpful here:
- Deontological Theories and Metaethics
Deontological theories are normative theories. They do not presuppose any particular position on moral ontology or on moral epistemology. Presumably, a deontologist can be a moral realist of either the natural (moral properties are identical to natural properties) or nonnatural (moral properties are not themselves natural properties even if they are nonreductively related to natural properties) variety. Or a deontologist can be an expressivist, a constructivist, a transcendentalist, a conventionalist, or a Divine command theorist regarding the nature of morality. Likewise, a deontologist can claim that we know the content of deontological morality by direct intuition, by Kantian reflection on our normative situation, or by reaching reflective equilibrium between our particular moral judgments and the theories we construct to explain them (theories of intuitions).
Nonetheless, although deontological theories can be agnostic regarding metaethics, some metaethical accounts seem less hospitable than others to deontology. For example, the stock furniture of deontological normative ethics—rights, duties, permissions—fits uneasily in the realist-naturalist's corner of the metaethical universe. (Which is why many naturalists, if they are moral realists in their meta-ethics, are consequentialists in their ethics.) Nonnatural realism, conventionalism, transcendentalism, and Divine command seem more hospitable metaethical homes for deontology. (For example, the paradox of deontology above discussed may seem more tractable if morality is a matter of personal directives of a Supreme Commander to each of his human subordinates.) If these rough connections hold, then weaknesses with those metaethical accounts most hospitable to deontology will weaken deontology as a normative theory of action. Some deontologists have thus argued that these connections need not hold and that a naturalist-realist meta-ethics can ground a deontological ethics (Moore 2004).
I think there’s a confusion in our discussions of deontology and consequentialism. I’m writing this post to try to clear up that confusion. First let me say that this post is not about any territorial facts. The issue here is how we use the philosophical terms of art ‘consequentialism’ and ‘deontology’.
The confusion is often stated thusly: “deontological theories are full of injunctions like ‘do not kill’, but they generally provide no (or no interesting) explanations for these injunctions.” There is of course an equivalently confused, though much less common, complaint about consequentialism.
This is confused because the term ‘deontology’ in philosophical jargon picks out a normative ethical theory, while the question ‘how do we know that it is wrong to kill?’ is not a normative but a meta-ethical question. Similarly, consequentialism contains in itself no explanation for why pleasure or utility are morally good, or why consequences should matter to morality at all. Nor does consequentialism/deontology make any claims about how we know moral facts (if there are any). That is also a meta-ethical question.
Some consequentialists and deontologists are also moral realists. Some are not. Some believe in divine commands, some are hedonists. Consequentialists and deontologists in practice always also subscribe to some meta-ethical theory which purports to explain the value of consequences or the source of injunctions. But consequentialism and deontology as such do not. In order to avoid strawmaning either the consequentialist or the deontologist, it’s important to either discuss the comprehensive views of particular ethicists, or to carefully leave aside meta-ethical issues.
This Stanford Encyclopedia of Philosophy article provides a helpful overview of the issues in the consequentialist-deontologist debate, and is careful to distinguish between ethical and meta-ethical concerns.
SEP article on Deontology