I'm a holist about rationality. That is, I agree with Julian Nida-Rumelin that it would be "perfectly rational to refrain from point-wise optimization because you do not wish to live the life which would result." Rationality involves abstraction. In particular, the rational decision is one that you would endorse from a timeless perspective. The answer to what you should do at any given moment derives from the broader question of how you want your whole life to go. Now, I want to defend an analogous holism about ethics.
The essence of ethical holism, as I conceive of it, is that individual rights and duties derive from the broader facts about what is desirable for society as a whole. This holistic approach to ethics is exemplified by my "institutional" theory of rights. It extends beyond merely legal rights, however -- indirect utilitarianism may likewise lead us to promote various social norms or duties that cannot be legally enforced.
An interesting application of ethical holism is to the question of 'boycotting the needy'. Let us assume that the institutions of prostitution and sweatshops make the world a better (i.e. slightly less miserable) place. The desperate people employed there are better off than they would be if deprived of this option. But then ethical holism suggests the following principle deriving permissibility from good institutions:
(PGI): If an institution is desirable, then people do not have a general obligation to refrain from participating in (or otherwise supporting) it.
This seems a very plausible principle. There is something incoherent about the views of someone who grudgingly approves of the institution of prostitution (because it makes the women involved better off than they would otherwise be) and yet insists that it is morally impermissible for Johns to do business with them. You know, "he who wills the end, wills the means," and all that. If you support a general policy, you must allow people to implement it. Hence, to condemn the participants, you must first denounce the general policy. It is this broader level that the holist asks us to focus on.