The critique by Mills is less of Rawls here than what Rawlsianism has become, or perhaps could only have become:
Rawls himself said in the opening pages of “A Theory of Justice” that we had to start with ideal theory because it was necessary for properly doing the really important thing: non-ideal theory, including the “pressing and urgent matter” of remedying injustice. But what was originally supposed to have been merely a tool has become an end in itself; the presumed antechamber to the real hall of debate is now its main site. Effectively, then, within the geography of the normative, ideal theory functions as a form of white flight. You don’t want to deal with the problems of race and the legacy of white supremacy, so, metaphorically, within the discourse of justice, you retreat from any spaces worryingly close to the inner cities and move instead to the safe and comfortable white spaces, the gated moral communities, of the segregated suburbs, from which they become normatively invisible….
Rather, mainstream political philosophy is seen as irrelevant to [e.g., forums on race and civil rights] because of the bizarre way it has developed since Rawls (a bizarreness not recognized as such by its practitioners because of the aforementioned norms of disciplinary socialization). Social justice theory should be reconnected with its real-world roots, the correction of injustices, which means that rectificatory justice in non-ideal societies should be the theoretical priority, not distributive justice in ideal societies. Political philosophy needs to exit Rawlsland — a fantasy world in the same extraterrestrial league as Wonderland, Oz and Middle-earth (if not as much fun) — and return to planet Earth.