There are numerous problems with Rawls's contention here. Wolterstorff sums some of them up.
Suppose, then, that someone has followed that strategy; she has analyzed our political mentality into its constituent ideas and has elaborated these ideas into principles of justice. I submit that no matter what those resultant principles of justice may be, the reasonable thing for her to expect is not that all reasonable people who use their common human reason will agree with her results, but that not all reasonable people will agree. It would be utterly unreasonable for her to expect anything else than disagreement. The contested fate of Rawls’ own principles of justice is an illustrative case in point. There’s no more hope that all those among us who are reasonable and rational will arrive, in the way Rawls recommends, at consensus on principles of justice, than that we will all in the foreseeable future, agree on some comprehensive philosophical or religious doctrine. [Emphasis original]Here Wolterstorff emphasises two points. Firstly, he suggests that the contents of public reason are such that it is to be expected that reasonable people will disagree over them. Secondly, Wolterstorff hints that this renders Rawls's position incoherent. Rawls rejects appeals to comprehensive doctrines because people can reasonably reject them and there is a duty to not decide questions of basic justice this way. If this is true then we should reject appeals to public reason as well; in fact, we have a duty to not follow public reason. However, if we cannot follow public reason and we cannot follow comprehensive doctrines, we are left with nothing; few restrictive laws or policies could be morally justified. This is precisely the implication that Quinn suggested.
Wolterstorff's argument depends on his claim that it is reasonable to expect disagreement over the contents of public reason. He cites Rawls's own theory of justice in support of this. In A Theory of Justice, Rawls attempts to develop an account of basic justice based on public reason. However, there is widespread disagreement amongst reasonable people not only over the conclusions reached but the methods and implicit principles themselves.
Of course, merely appealing to one case is unpersuasive; it is possible this is a single anomaly. However, in an earlier work Wolterstorff cited other examples where public reason appeared unable to be used in a manner that would be agreed upon by reasonable people. In “The Role of Religion in Political Issues,” Wolterstorff cites the work of Kent Greenawalt to illustrate that not only is public reason incapable of resolving questions of contentious political issues but also on many issues it is “simply irrelevant”, public reason has “nothing to say”.
For example, Wolterstorff refers to the debate about whether the state has a duty to provide social welfare. In this debate not only is there disagreement about the conclusions but also debate about the very basic principles or concepts involved. Both supporters and opponents of state welfare appeal to such things as ‘freedom’ and ‘equality’ but have radically different conceptions as to what freedom and equality are. Also involved in this debate are different assumptions about whether there are property rights and if there are, how such rights are weighed against social utility. It is unlikely that the consensus populi, common sense and uncontroversial science provide answers to these questions that all reasonable people would accept.
Wolterstorff is not alone in these observations. Christopher Eberle makes similar observations about such things as abortion and freedom of religion. De Marneffe argues that on contentious moral and social issues public reason will fail to offer any substantive answer. Jean Hampton suggests that public reason cannot provide an answer to the question of abortion. Quinn makes similar observations. The point is, that if we genuinely limit ourselves to principles upon which no reasonable person can be expected to reject, what we are left with is inadequate to provide answers to many, if any, substantive questions. Only if we supplement these with premises drawn from some comprehensive doctrine will answers be adequate.
The case of abortion that these authors refer to is particularly instructive. Rawls’s own comments on this issue unwittingly confirm this. When discussing how public reason would address the question Rawls simply asserts that reasonable people will agree that in the early stages of pregnancy the right to equality overrides our due concern for human life. However, he seems to countenance the idea that reasonable people may limit abortion in the second trimester in certain circumstances. Now this, clearly, is not an obvious intuition shared by all reasonable people - unless one wishes to stipulate ‘reasonableness’ to rule out anyone who does not hold Rawls’s substantive normative views on abortion.
Moreover, it appears that one cannot adjudicate any dispute between Rawls and a critic on this issue without appealing to a comprehensive doctrine. Suppose, for example, that a fetus is a person in the first trimester of pregnancy then Rawls’s suggestion that the value of equality overrides in the first trimester but may not always in the second is false. Why would it be acceptable in the name of equality for a woman to kill a person in one trimester and not the other in otherwise identical circumstances? It seems that Rawls’s intuition is justified only if one assumes that a first trimester fetus is not human. On the other hand, if one assumes that a fetus is human at this point then Rawls’s position is erroneous. Hence, only by addressing this issue can such a debate be settled.
However, addressing this issue by appealing to public reason or common sense can hardly provide an answer. As Quinn notes, “common sense is divided on or simply perplexed on the question of abortion”. Uncontroversial science can tell us facts of fetal development but it cannot tell us the moral significance of those facts or what facts are important for determining personhood. In addition, there is no consensus populi on this issue; the political culture of many countries is divided on this question. It seems impossible to offer any argument one way or the other without utilising a premise drawn from some comprehensive doctrine over which reasonable people do not agree.
Similar points apply to Rawls's claim that a right to abortion is necessary so as to give the right to equality “substance and force”. This follows only if one assumes a particular understanding of equality yet neither the consensus populi nor common sense will produce this conclusion. In fact, it is arguable that much of the popular appeals to equality are confused and ambiguous. Moreover, even if such a consensus on the nature of equality were available, it does not follow that a right to abortion is necessary for giving it force unless one supplements this concept with understandings of sexuality and gender drawn from some comprehensive perspective.
I do not think abortion is an isolated case. The same would apply to other substantive questions such as homosexual marriage, affirmative action, capital punishment, welfare, etc. Wolterstorff’s contention that public reason will not, un-supplemented with comprehensive doctrines, provide information that all rational people can be reasonably expected to accept or even provide an adequate base for deciding many substantive issues appears justified. If this is so, Rawls’s position is incoherent or ad hoc.
 Wolterstorff, “Why We Should Reject What Liberalism Tells Us,” 174.
 I am grateful for discussions with Dr Glenn Peoples for helping me to develop this argument.
 John Rawls, A Theory of Justice, (Cambridge MA: Harvard University Press, 1971).
 Wolterstorff, “The Role of Religion in Political Issues,” 102-104.
 Ibid., 102.
 Ibid., 103-104.
 Eberle, Religious Conviction in Liberal Politics, 217-222.
 de Marneffe, “Rawls’s Idea Of Public Reason,” 232-250.
 Jean Hampton, “The Common Faith of Liberalism,” Pacific Philosophical Quarterly, 75 (1994), 208-209.
 Quinn, “Liberalism and Their Exclusions of the Religious,” 149-150.
 See Louis Pojman, “Theories of Equality: A Critical Analysis,” Behavior and Philosophy 23:2 (1995): 1-27, and his “Equal Human Worth: A Critique of Contemporary Egalitarianism.” http://22.214.171.124/search?q=cache:CvaEU_1lw5IJ:www.louispojman.com/equalworth.pdf+Equal+Human+Worth+Pojman&hl=en&gl=nz&ct=clnk&cd=8.
 See de Marneffe, “Rawls’s Idea of Public Reason,” 234-235.
Rawls on Religion and Public Life Part 1
Some More Thoughts on Religion and Public Life: Robert Audi’s Critique of Wolterstorff