I've always thought that Gandhi, King, and Mandela, the multiculturalists' holy trinity, were highly overrated. Their chief virtues were their bravery--it takes some guts to stand up against the authorities when you're a member of what they consider an inferior group--and Gandhi's and King's non-violence. Mandela, notoriously, approved of violence.
However, none of the three was particularly altruistic--each worked toward the benefit of his own people, just like any other nationalist does. We're not talking Wilberforce or Henry Ward Beecher, members of the dominant group who worked for the rights of the dominated group. Or Lyndon Johnson and Earl Warren, who did much more to put an end to Jim Crow than King did. Johnson rammed literally dozens of civil rights laws down Congress's throat, and Chief Justice Warren backed him all the way. Or Eisenhower; when Little Rock tried to defy the Supreme Court and maintain segregated schools, Ike sent in the Airborne and Arkansas got the idea that things had changed.
Also, working against a system that does bad things does not necessarily make you a good person. Look at the Communists around the world. Sure, here in Spain they opposed Franco, and Franco was a bad guy, but the Communists were just as bad and might have been even worse. We're not talking about a democratic opposition or intellectual dissidents here.
Finally, Gandhi, King, and Mandela were fighting British imperialism, American Jim Crow, and South African apartheid, respectively. All bad things, I will agree, and they are all happily long gone. But these three men were dealing with more or less civilized opponents, who shrank from using extreme violence and repression. None of them would have lasted five minutes under Stalin, Mao, Hitler, Castro, Ho, Kim, or Saddam. Or even such comparatively mild dictators as Mubarak, Pinochet, or the king of Morocco.