“Now it is worth noticing two things about the private substitutes that I have described. The first is that in the aggregate they are probably much more expensive than would be the implementation of the appropriate public policy. The second is that they are extremely poor replacements for the missing outcomes of good public policy. Nevertheless, it is plain that the members of a society can become so alienated from one another, so mistrustful of any form of collective action, that they prefer to go it alone.”