Pluralistic ignorance
In social psychology, pluralistic ignorance is a situation in which a majority of group members privately reject a norm, but go along with it because they incorrectly assume that most others accept it. This is also described as "no one believes, but everyone thinks that everyone believes". In short, pluralistic ignorance is a bias about a social group, held by the members of that social group.
Multiculturalism
Providence has been pleased to give this one connected country to one united people – a people descended from the same ancestors, speaking the same language, professing the same religion, attached to the same principles of government, very similar in their manners and customs... This country and this people seem to have been made for each other, and it appears as if it was the design of Providence, that an inheritance so proper and convenient for a band of brethren, united to each other by the strongest ties, should never be split into a number of unsocial, jealous, and alien sovereignties.
As a philosophy, multiculturalism began as part of the pragmatism movement at the end of the nineteenth century in Europe and the United States, then as political and cultural pluralism at the turn of the twentieth. It was partly in response to a new wave of European imperialism in sub-Saharan Africa and the massive immigration of Southern and Eastern Europeans to the United States and Latin America. Philosophers, psychologists and historians and early sociologists such as Charles Sanders Peirce, William James, George Santayana, Horace Kallen, John Dewey, W. E. B. Du Bois and Alain Locke developed concepts of cultural pluralism, from which emerged what we understand today as multiculturalism. In "Pluralistic Universe" (1909), William James espoused the idea of a "plural society." James saw pluralism as "crucial to the formation of philosophical and social humanism to help build a better, more egalitarian society.