John Rawls went boldly where everybody had gone before and became famous for that. The only problem is that the crown jewel of his thought was, well, wrong.
We've discussed this before: one of the many ways people can be sliced is through the filter of Rousseau vs. Hobbes. For Rousseau fans, when humans were hunter-gatherers it was an idyllic era of peaceful coexistence, abundance and happiness. For those more of the Hobbes inclination, instead, the earlier humans had a brutish and short existence. A quick read of, for example, Azar Gat's War in Human Civilization suffices to reasonably tilt oneself towards a Hobbesian worldview, for humans have been massacring each other (as much as cooperating) since time immemorial. And, with that, humans have also been asking each other: how is it that we stay together in groups and how could we build a good society? This is what kids these days get indebted for when they go for a degree in political science, mind you.
Instead of thinking about the state of nature, or whether it was paradise or a living hell, Rawls went into the long tradition of social contract thinkers armed with a hypothetical situation known as the original position. In such a thought experiment, a bunch of people come together while placed behind a veil of ignorance (i.e. not knowing their ethnicity, sex, status, or conception of the good) and try to rationally decide the basic structure of the society they will live in. Since they are ignorant of themselves, they draft their social contract as impartially as possible because they don't know what end of the stick will they end up with. This is all cool and the gang but there are two grave flaws when trying to use the original position. One problem I will call Nozickian while the other I shall call Scrutonian, though one leads to the other.
Robert Nozick, a beast of a philosopher --at least to my taste-- wanted nothing to do with the original position. As Nozick intuitively stated, the only transaction that is just in and of itself is a voluntary one, thus it follows that, as history develops, each person's abilities end up with unequal outcomes, making it antithetical to an original position which is, by definition, ahistorical. The subjects in Rawls' thought experiment have had, in Nozick's view, their cojones chopped off. Since they have no clue what hand they have, they're risk averse and, thus, scores will be settled with the passing of time, depriving the original position of its effectiveness as a desirable model in terms of fairness, liberty, and, again, historical depth.
This brings us to Roger Scruton and the huge oversight in Rawls' thought experiment. For Scruton, when the individuals come to the original position, they have already made, by just being there, a decision --one which invalidates any veil of ignorance, i.e. they have taken the step of deciding that the first person plural of their community is needed and desirable. By means of what it shares with others of the same species, there is simply no way an equally cooperative and murderous animal as the human will come together without a basic layer of trust underneath. The attributes or ideals upon which that trust is built have such a weight that Nozick's historicity becomes a crucial element in dismantling Rawls from the get go.
And this is where Rawls' thought experiment dismantles either as naive or insidious. Humans aren't a blank slate. By the mere act of being born they come with a "hardware" and a "pre-installed software" that play a huge role in their worldview and, thus, behavior. As time progresses and communities form, the individual abilities reflected through the governance of particular societies necessarily sets them apart form each other in certain aspects while unearthing commonalities which are a product of their shared "hardware" and "software". The interaction of all these factors, and the different communities that form within themselves and each other, are thrown into the big laundry machine of history, with a dash of good ol' circumstance, and the outcome may be war or peace.
If read in a conspiratorial manner, Rawls is guilty of utopianism. And trying to build an ideal society always ends up in chaos and carnage, mind you. Humans aren't Play-Doh™ figurines that can be sculpted into whatever is desired. For millions of years, and particularly since gaining consciousness, humans have been slaughtering each other at the same time that they display an astonishing ability for cooperation. The former has kept them from conquering the universe while the latter allowed them to conquer the world. Tinker with what is built at your own peril.