What is Dr. Forbe’s issue with the U. S using American or America excusably?

Dr. Forbe raises in his essay the fact that the demonym "American" or the name "America" as the name of the nation are restrictive and incorrect, since America as such is actually an entire continent, spanning from Canada to the north to Argentina in the south. Thus, using the name America for the United States of America is in fact a mistake, since it displaces the other nations of the continent from the status of Americans.

The same occurs with the different ethnicities and nationalities that make up these nations, since, for example, a person from Argentina is both Argentine and American, thus restricting the demonym to people from the United States of America is, at least, totally arbitrary.