The 1967 release of Harold Cruse's book The Crisis of the Negro Intellectual isolated him from almost all other scholars and activists of the American Civil Rights Movement--though many of those thinkers disagreed with each other, he nonetheless found ways to disagree with them all. He thought that activists who believed that Black people such as himself should culturally assimilate were naive. But he also sharply criticized Black nationalists such as Marcus Garvey, who wanted to establish independent, self-contained Black economies and societies, even though Cruse himself identified as a Black nationalist.

Which choice best describes the function of the underlined sentence in the text as a whole?