Realistic Utopia, a fantasy?

Some may object to Rawls's idea of a reasonably just constitutional democratic society by insisting that this type of society is purely fantasy. Dreadfully evil events, like the Holocaust and the Inquisition for instance, prove that the hopes expressed by Rawls's realistic utopia are fantastic.

Rawls presents an awkward argument to defend himself against this objection. He wants to show that the past and present evils fail to undermine hope for the future of a society as belonging to a Society of liberal and decent Peoples (Law of Peoples, p. 22f).

Ultimately, his argument rests on the idea of the "reasonableness" of the Law of Peoples. There are two ways we could interpret "reasonableness." The first way is that any reasonable person would agree that x is reasonable. There is something fundamentally true or fundamentally valuable about x that makes it reasonable. The second way is that given a, b, c, etc., x is reasonable. In this case, reasonable means that if certain conditions are met, then we consider x the most plausible or most reasonable.

If Rawls uses the first sense of reasonable, then his view has not addressed the fantasy charge. If Rawls uses the second sense of reasonable, then his view fails to have any force. Rawls's idea of "reasonableness" is not clear.