People study history for very varied reasons but among them the most important reasons are to reveal past contributions of civilazation so that we can connect the past to the present. It is also important to take notes of different scenarios so that we can create the greater pictures.
Segregation was okay as long as everything was " seperate but equal".
Though, Plessy and Jim Crow did give the NAACP and other black groups something specific to fight against later for equality (Brown vs. the Board of Ed.)
While Muslims and Hindus did peacefully coexist in many parts of India for a long time, the two groups could, and did, turn against each other as a result of the economic, social, and military conflicts of the age