On traditional analysis accounts rooted in the essentialism originating with Socrates and Plato, definitions are indeed neither held to be assertions nor have truth values. They are mere descriptive statements. But this is controversial. Thus the correct definition is the accurate description. But what is an accurate description? From the Encyclopedia of Philosophy's entry on Definition:
"[P]aradoxically, no problems of knowledge are less settled than those of definition, and no subject is more in need of a fresh approach. Definition plays a crucial role in every field of inquiry, yet there are few if any philosophical questions about definition (what sort of thing it is, what standards it should satisfy, what kind of knowledge, if any, it conveys) on which logicians and philosophers agree.
Thus, the notion that a real definition should be presumed and not an instance of assertoric force nor possessing any truth-conditional semantics, is a particular flavor of definition, one related to certain metaphysical presuppositions of object and objective, both of which are philosophically controversial notions. If one believes there is an objective reality, than a definition isn't lexical in the classical sense, but is a mere description of what is. Kant raised the question with his Ding-an-sich created philosophical complications related to claiming that we know only appearances, and not actuality. There was, of course, strong pushback:
The obvious SEP article to begin with is Definitions. From the SEP:
For the Frege-Russell project to succeed, the definitions used must have a special character. They must be conceptual or explicative of meaning; they cannot be synthetic. It is this kind of definition that has aroused, over the past century or so, the most interest and the most controversy.
What is controversial is the ontological ambiguity that modern philosophy seems to acknowledge. For instance, the logical positivists failed to produce any procedure that would allow one to produce objective observation statements divorced from theoretical content related to a modern account of theory-ladenness. If one's views are always contaminated or normative, there can be no objective description at all. Thus, on this view, there can be no real definition at all. Which brings us to our second topic the SEP covers, Concepts which are presumed to be that which real definitions allude to:
Concepts are the building blocks of thoughts. Consequently, they are crucial to such psychological processes as categorization, inference, memory, learning, and decision-making. This much is relatively uncontroversial. But the nature of concepts—the kind of things concepts are—and the constraints that govern a theory of concepts have been the subject of much debate
Again, we find that metaphysics has great bearing on definition, if definitions, as Locke held, are related to thoughts, concepts, or as he referred to them, Ideas. For instance, there is strong empirical evidence to doubt the classical theory of concepts. Again from the SEP:
The classical theory has come under considerable pressure in the last forty years or so, not just in philosophy but in psychology and other fields as well. For psychologists, the main problem has been that the classical theory has difficulty explaining a robust set of empirical findings. At the center of this work is the discovery that certain categories are taken to be more representative or typical and that typicality scores correlate with a wide variety of psychological data
You say:
In spite of this, the above form of argument is so common I think there should be a compact name for it, to refer people to. Is there any Stanford Encyclopedia of Philosophy article that elaborates on the fallacy of treating definitions as if they are assertions.
Therefore the argument is common, not because it is widely recognized as fallacy, but because the notion that definitions are objective descriptions of reality without truth conditions, as in the classical notion of real definition, is itself controversial. Robinson's work Definition adheres to the classical notion going so far as to claim that real definitions are not definitions at all in the sense of lexical definitions. But, post-positivist thinking strongly undermines this claim, such as in the works of Sellars and McDowell who go so far as to argue that the spontaneity of sensory impressions are themselves not objective therefore rejecting them as empirical experience, a notion known by the Myth of the Given.
Given the sophistication of the argument, and the breadth of positions required to understand conceptualism, for instance, it often comes as a surprise to many to find that essentialist notions of definition are actually controversial. A similar pattern of surprise occurs to mathematicians who are frequently raised on a steady diet of Platonic thinking and then come to find that intuitionists in mathematics (SEP) reject core metaphysical presumptions of the objectivity of mathematics.
Thus, the position you cite is common not because it is fallacious, but because it contests your metaphysical presuppositions to begin with. Given the strength of both positions, to count one or the other is polemical, because both notions of definition have more than adequate metaphysical grounding. Rather, what you are witnessing is the schism inherent in the realist/anti-realist debate in ontology. We anti-realists simply do not agree to the "universal objectivity" of observation and definition you presume, and often reject certain key distinctions like the analytical-synthetic and the fact-value.
