Bryan Caplan asks the normative question, "Is anyone willing to often even a semi-plausible economic argument in defense of mandatory national origin labels?"
I'm not. But I do have an answer to this positive question: what is the origin of national origin labels? In the United States, it's labor union racism. Here's what Morgan Reynolds wrote in his Concise Encyclopedia of Economics article, "Labor Unions":
Economist Ray Marshall, although a prounion secretary of labor under President Jimmy Carter, made his academic reputation by documenting how unions excluded blacks from membership in the 1930s and 1940s. Marshall also wrote of incidents in which union members assaulted black workers hired to replace them during strikes. During the 1911 strike against the Illinois Central, noted Marshall, whites killed two black strikebreakers and wounded three others at McComb, Mississippi. He also noted that white strikers killed ten black firemen in 1911 because the New Orleans and Texas Pacific Railroad had granted them equal seniority. Not surprisingly, therefore, black leader Booker T. Washington opposed unions all his life, and W. E. B. DuBois called unions the greatest enemy of the black working class. Another interesting fact: the "union label" was started in the 1880s to proclaim that a product was made by white rather than yellow (Chinese) hands. [emphasis mine]