The truth is that human rights law has failed to accomplish its objectives. There is little evidence that human rights treaties, on the whole, have improved the wellbeing of people. The reason is that human rights were never as universal as people hoped, and the belief that they could be forced upon countries as a matter of international law was shot through with misguided assumptions from the very beginning.
He argues that human rights treaties do not seem to influence the behavior of government, that human rights law is so "hopelessly ambiguous" that governments can rationalize anything under it, and that such laws tend to express arrogance more than idealism. His alternative is to focus on wellbeing:
It is time to start over with an approach to promoting wellbeing in foreign countries that is empirical rather than ideological. Human rights advocates can learn a lot from the experiences of development economists – not only about the flaws of top-down, coercive styles of forcing people living in other countries to be free, but about how one can actually help those people if one really wants to....Helping other countries means giving them cash, technical assistance and credit where there is reason to believe that these forms of aid will raise the living standards of the poorest people.
And he ends with the insistence, "A humbler approach is long overdue."
There are a number of problems with the argument. It is noticeable that the criticism of human rights law from the beginning was that it doesn't improve wellbeing, so it seems a little peculiar that wellbeing projects are themselves the alternative; and rather suspicious that while human rights law is criticized for not being a wellbeing project, there is neither a hint nor shadow of recognition of the fact that someone could question whether wellbeing projects improve situations from the perspective of human rights. Human rights law is criticized both for being imposed on governments and for not influencing government behavior; and, for that matter, it is criticized for not influencing government behavior and for being the language governments go out of their way to use in order to justify themselves.
There is simply no sense in which focus on wellbeing is a "humbler approach" than human rights law. Wellbeing projects are notorious for being forced on local populations who do not need them or cannot use them. Some wellbeing projects have excellent results. Others destroy the local economy and create new problems on top of the old ones that they failed to fix. Posner notes that a lot of studies of wellbeing projects have been done, and touts the empirical approach as a good one; what he doesn't say is that most of those studies show that a very large portion of those projects fail even in their particular objectives. What is more, a project that works very well in one place may fail miserably in another. It takes a lot of work, and a lot of local cooperation and initiative, to make these things succeed at all. Indeed, for them to be successful, they primarily have to be powered by local efforts in the first place, with the aid and assistance just supplementing what those local efforts are doing.
If one insists on the importance of scale, a human rights approach can be handled on a small scale. This is what International Justice Mission does, for instance, defending individuals and working with local governments, and it is only one organization of many. Posner focuses almost entirely on large scale treaties. But most of those were never intended to do the substantive work, but only to lay down the general lines.
So, in other words, whether or not human rights approaches are worthwhile, there seems to be no good reason to think that Posner's proposed alternative actually fares any better, even according to some of his own criteria. If we are considering particular cases in which wellbeing projects succeed, there are particular cases in which human rights law succeeds; if we are considering the failure of human rights law to contribute to wellbeing in general, wellbeing projects, rather ironically, apparently fail to contribute to wellbeing in general. And it's ironic that he ends by comparing the hubris of human rights law to the hubris of nineteenth-century "civilising efforts", since the latter were certainly thought of in terms much more like the "humbler" wellbeing project than they were thought of in terms like human rights law. That Posner chooses to name his proposed civilizing efforts 'wellbeing promotion' scarcely changes what he seems to be proposing, however humbly he conceives of them, unless he just means 'give local people some occasional help in doing what they already happen to be trying to do'.