Part III of Stephen Carter's The Violence of Peace: America's Wars in the Age of Obama deals with "The Rights and Dignity of Strangers," particularly asking questions about a country's moral obligation to intervene on behalf of others. He addresses the genocide that has taken place in Rwanda and Darfur (and Bosnia before that) and juxtaposes one's responsibility to act (a responsibility that the WWII allies put upon themselves with the Convention on the Prevention and Punishment of the Crime of Genocide in 1948) with pacifism.
A decision to intervene in the affairs of another country is no doubt in the end a matter of politics. But the arguments for it are moral. Not every form of government is equal. One thinks here of Reinhold Niebuhr: "Pacifism either tempts us to make no judgments at all, or to give an undue preference to tyranny in comparison with the momentary anarchy which is necessary to overcome tyranny." ... Whatever the attraction of pacifism when you alone are under threat, there is less virtue in being pacifist when called upon to defend someone else.
Carter's point is a tough one to combat. For indeed, it is one thing to choose not to defend yourself when you are being attacked on the grounds of pacifism, but it is another entirely to stand by and watch others (whether one, thousands, or millions) be attacked (raped, killed, slaughtered) and do nothing because you are a pacifist.
Is pacifism, then, really a virtue? How do the examples of Gandhi and King play into your answer?