I think that there is much to be said for Heiner's approach,  which is deeply rooted in Hayek's works. Private law has no purpose, not even the promotion of wealth maximization, certainly not the wealth maximization of "Society". The whole Posnerian appraisal clashes with Hayek's.
The only purpose of law (as distinguished from legislation) is to ensure the overall order, i.e. the law indeed does not serve any single purpose, but rather countless different purposes of different individuals  It provides only the means for a large number of different purposes that as a whole are not known to anybody. In the ordinary sense of "purpose", law is not therefore a means to an end, but merely a condition for the successful pursuit of most purposes.
The best spontaneous order is that of the price system, because prices convey to us information about how unknown people have reacted to unknown circumstances using their own particular knowledge of the situation. The price system that conveys such information allows the sharing of widespread knowledge in society among millions of different people who need not contact each other to cooperate. It allows the formation of a spontaneous order of actions. Law is a condition of this system patently based on property, tort and contract. But these legal institutions are important not because they maximize anything, but because we cannot know in advance which use will be made of rights possessed by individuals, and so we cannot know in advance which purpose will be served. That is why law based on "classical" property, tort and contract doctrines is the law of liberty, and after all, liberty is interesting precisely because we cannot predict its use.
As a consequence, of course, legal analysis cannot be reduced to a single method of approaching the law. Judges are not to shape the legal order. They always find such an order in existence as an attribute of an ongoing process in which individuals are able successfully to pursue their plans because they can form about the actions of their fellows expectations which have a good chance of being met. In deciding disputes, I should say in "deciding appeals", and in endeavouring to articulate and improve rules of just conduct, judges are called to correct disturbances in the legal order.
It follows also from this picture that the law, in the sense of the "lawyers' law", exists independently of any single group of minds committed to shape society, and it rests not only on economic ideals but also on a diffuse opinion of what is right.
These are all economic (Austrian) reasons not to reduce legal analysis to mere Law and Economics. That same price system is the most striking example of how great economic achievements may be reached through institutions no one consciously designed to achieve results of maximization. In the same sense, the achievement of precise outcomes may be the task of the law of legislation, but the establishment of rules independent of particular outcomes is the general purpose of lawyers' law as an overall orderer of society.
Maybe this is all a fable of Austrian bees. But it is much more consistent not only with our tradition, but also with an analysis of law, attitudes and beliefs in terms of the order resulting from the shaping and reshaping of property rules and liability rules, than the illiberal ideal of wealth maximization as a value in determining the precise outcomes of particular cases.
1 114 So. 2d 357 (Fla. Dist. Ct. App. 1959).
2 See the discussion of the case in Barnes & Stout, Cases and Materials in Law and Economics 43ff. (1992).
3 Matthew 25:29
4 See how Calabresi shew the arbitrariness of these assuptions in Calabresi, Do We Own Our Bodies ?, in B.M.Dickens (ed.), Medicine and the Law, Dortmouth, 1993, 5 ss.
5 A.K.SEN, The Impossibility of a Paretian Liberal, 78 Jo. of Political Economy, 152-7 (1970).
6 R.A.HEINER,Imperfect Decisions and the Law: On Evolution of Legal Precedent and Rules, 15 JLS,227 (1986).
7 F.v.Hayek, Law Legislation and Liberty, I, Rules and Order 113 (1973).
8 Hayek, supra note 8, at 95.