First mainstream anthropology, under the influence of Franz Boas, came to reject the concept of race as having explanatory power. Some decades latter the American Anthropological Association (AAA) and the Canadian Anthropological Society (CASCA), have now cancelled sex as well: “There is no single biological standard by which all humans can be reliably sorted into a binary male/female sex classification,” it reads. "On the contrary, anthropologists and others have long shown sex and gender to be historically and geographically contextual, deeply entangled, and dynamically mutable categories." Well, what is a social construction is sociology and anthropology, pseudosciences at best.
The idea here is that sex and gender are not binary, but pure social constructions. These are the same body of arguments used against race, and as these arguments against sex can be shown to be flawed, the arguments against race also fail.