One of my ultimate pet peeves is people replacing the reality of justice with the perceived capacity to obtain it. By this, I mean folks who argue for a particular definition or conception of justice specifically on the grounds that it would be attainable, or against alternative conceptions because they have no identifiable stopping point. An "attainable" philosophy is one that we can realistically imagine "completing", so there is nothing left to do. An unattainable philosophy, by contrast, is not necessarily a futile one, it just means that its conceptual endpoint probably will never be reached. For example, "nobody should (unwillingly) die of illness" is an unattainable philosophical position -- we probably will never reach a point where nobody dies of a disease. But we can still move towards that reality, by making it progressively less likely that people will die of disease. Someone wedded to the idea of attainability, however, would argue that beyond some point it is no longer unjust when people die of disease -- there is an achievable "limit" at which point the requirements of justice have been met. Demands beyond that are unreasonable insofar as they effectively posit that we can never have a completely just health-care system.
This mode of argumentation pops up all the time. For example, liberals attack the sufficiency of negative liberty by noting that non-interference does not equalize the ability to act -- in a completely open world, some people can do many more things than others. If freedom implies access to at least a certain bundle of resources and privileges necessary to pursue one's desired ends in the public sphere, then the state must be enlisted to guarantee at least these minimums so people have the basic ability to act freely. In response to this argument, Raymond Plant articulates the conservative objection:
[F]reedom and ability cannot be the same thing, since no one is able to do all that he or she is free to do. I am free to do everything that I am not currently prevented by others from doing. Thi will turn out to be an indefinitely large number of things. However, it does not matter how rich and powerful or how intelligent or resourceful I am, it still remains the case that I am able to do only a small number of things that I am free to do.... There is no way in which abilities, capacities and powers can be equalised, and therefore if freedom is understood at least in part in terms of ability then we can never attain the liberal ideal of equal freedom, an ideal which can be attained if by freedom we mean mutual non-coercion. [Raymond Plant, "Neo-liberalism and the Theory of the State: From Wohlfahrtsstaat to Rechtsstaat," The Political Quarterly Vol. 75, pp. 24-37 (2004), 26]
Similar arguments are made by conservatives against color-conscious policies designed to increase diversity, which Justice Scalia has protested could be justified indefinitely; and in favor of jurisprudential techniques like originalism, which are praised for supposedly being concrete, definite, and definitive. It's barely even acknowledged that justice might require a degree of uncertainty, fluidity, or flexibility. What if racial justice does require indefinite use of color-conscious selection processes? Should we care?
I won't say I don't understand the motivation behind the instinct. For understandable reasons, we want an attainable definition of justice, because to deny this forces us to run an exhausting and unending marathon chasing moral progress. We want to say we've "made it", and we can't, no matter how hard we try. Fine, and I'm sorry about that. Nonetheless, there is nothing implicit in the definition of justice that requires it to be concrete or attainable. Arguing that a particular mode of justice should be adapted simply because it's easier is intellectually facile and childish. Justice isn't a destination, it's a pursuit. That's the problem with ideals -- you'll find they're rather difficult to pin down in reality. If you're chasing an infinite like justice, you can never expect to get there. And if you construct your definitions with an end-point in time, you'll never realize those dimensions of justice which lie beyond the limit.
Because of that truth, I'd argue that restricting the discourse of justice to its realizable forms demonstrates not just a failure of moral fortitude and imagination, but a failure of morality itself. To return to the freedom-as-ability argument, I will freely concede that we will never reach a world in which everyone will be able to do everything. But it is ridiculous to use that observation as an argument in favor of not trying to expand the relative opportunities and abilities of individuals. The irony is that, as Plant puts it, the defense of the non-coercion model rests on the idea that we can claim -- definitively and concretely -- that the persons under it possess "equal freedom". Here is where radical communism intersects with radical capitalism -- being able to describe freedom as being held by all equally is more important than the actual material reality that people live in. But why should we care whether we can say that we've hit the ideal of equal freedom? Shouldn't we care more about actually being closer to it? The non-coercion theorists care more about being able to call the world just than trying to press for the maximum possible amount of justice. After all, if you're still pursuing justice, you're conceding that the current state of affairs contains injustice. And that's depressing!
The point, then, is twofold. First, attainability, by itself, is not an argument for a particular conception of justice. There is no reason for us to suppose we should be so lucky as to exist in a universe where justice is attainable. That might be a depressing thought, but past Elementary School "depressing" isn't a valid response to social reality. Second, adopting concrete models of justice is unnecessarily constraining -- it denies the reality of any dimensions of justice that lie beyond the limit, and thus consigns us to an inferior world so we can play make-believe that we live in a superior one. It can be scary to admit just how much there is left in front of us (an infinite amount, to be exact). But nobody denied that morality required courage.