Rawls thought that the principles of justice should apply to "the basic institutions of society", and was always slightly ambiguous about what this meant. Was it intended to mean coercive institutions - such as the state and particular distributions of property rights - or rule-giving institutions in general, such as marriage and religious authorities? The basic intuition in favour of the former view is that we usually want to avoid placing especially demanding political duties upon people beyond compliance with the basic laws and rules of society. If someone pays their taxes, drives on the correct side of the road, and avoids trespassing on the Royal Navy's battleships, then isn't that enough?
On the other hand, this seems to deny that considerations of justice might apply within the family. A hundred years ago this might have been seen as a virtue of the theory, but now that more-or-less everyone accepts that second-wave feminism was basically correct this view is hard to sustain. So if justice applies to individual actions in the context of family, why shouldn't it apply in a whole range of contexts?
One way of thinking about this is to consider what the origin of our moral duties is. (NB This need not be the same for all duties). I would broadly categorise the theories as such:
- Moral duties are pre-institutional. Political institutions, insofar as they are justified at all, exist as a mechanism to enforce the carrying out of these duties. Nozick can be seen as a paradigm case of this view, although it is consistent with a stronger conception of distributive justice: for example, I assume that Peter Singer would hold a view of this kind.
- Moral duties in some sense exist prior to institutions, but only become binding upon individuals when there exists a political community. Thomas Nagel holds a view of this sort, suggesting that it is unreasonable to expect individuals to deliberate as though their own interests are no more important than those of other people but that politics can act to achieve some form of equal consideration of interests.
- Moral duties come into existence only when there exists a political community. Hobbes would be the classical advocate of this view.
I would venture to suggest that (2) represents the mainstream view among political philosophers, at least with regard to issues of distributive justice. It has the advantage compared to (1) of explaining the particularity of our political obligations - of why individuals are attached to particular political institutions and not others. If you take (1) to be the case, it is hard to see how one can legitimise redistribution of income and wealth within the community without also legitimising global redistribution on the same scale - an implication that citizens of rich countries, including most political philosophers, are keen to avoid.
The disadvantage of (3) is that it is hard to explain why there are principles that all political institutions must follow. Whereas (2) suggests that political community simply activates pre-existing principles, (3) implies that the principles to be followed by a community are made anew each time a political community comes into being. This view fell out of fashion as communitarianism became less popular.
Nevertheless, all three views are somewhat popular within the discipline.
If you accept a view of type (1), then you will presumably think that the failure of a state to enforce a duty has no bearing upon whether or not one is morally obliged to comply with the duty. To take a duty where I think the truth of (1) is uncontroversial: one is obliged not to murder others, and this holds whether or not one will be punished for doing so.
If you accept a version of (3), then there is simply no way to say, outside of a particular context, what the duties of individuals are. This is not to say that there is no answer; rather, it means that this answer is one to be answered not through philosophical reflection upon the nature of morality, but through interpretation of a particular culture's practices.
But what about (2)? In this case we still do not know what the duties of individuals are, but in a different way from in (3). If (3) is true then it may be the case that members of a particular community have extensive moral duties, but this has little to no bearing upon what the duties of people in different societies are. If (2) is true, however, then people's duties should be more-or-less the same regardless of which society they inhabit.
This doesn't really answer the question, but I think it has helped to clarify my thinking on the topic. In particular, I am now aware of a couple of tensions in my beliefs. Firstly, I am attracted simultaneously to the views that there are limits to our duties, that there are some (admittedly small - I'm a sufficientarian, not an egalitarian) requirements of distributive justice, and the type (1) theory - that states should exist only to enforce pre-existing duties, and cannot create new duties. The joint coherence of these views is doubtful.
Second, in a part of this essay which I have deleted, I suggested that this might have to do with whether or not we conceive of justice as a substantive property or merely as the absence of injustice. I tend to believe the latter view, since surely injustice requires an actual victim rather than merely the potential to create victims? I thought that this might have some effect on which duties we still ought to respond to as individuals, but it is now not at all clear to me that this is the case.