Final answer:
Frederick Douglass's statement that 'all great qualities are never found in any one man or in any one race' supports the concept that diversity brings together a wider range of virtues and strengths, which is beneficial for a society.
Step-by-step explanation:
Douglass points out that "all great qualities are never found in any one man or in any one race" to argue that a combination of races is preferred to a single race. This statement encapsulates the idea that no single race possesses all virtues and strengths, and therefore, a diverse society that includes and values multiple races can draw from a wider array of talents and capabilities. The historical context given through references to Frederick Douglass and his views on diversity in America, alongside influential figures such as Sojourner Truth, Charles Sumner, and Martin Delany, highlights the ongoing struggle against racial discrimination and the movement towards recognizing the contributions of all races to American culture and progression.