John Rawls certainly has his fair share of critics, but he's also widely considered to be the most influential political philosopher of the 20th century. As we heard in the Rawls episode, Rawls's theory of justice is a kind of contract theory wherein he lays out the basic principles of a democratic society. In the same sort of way that his thought experiment asks us to assess the basic rules of society from behind a "veil of ignorance" in order to eliminate our particular biases, Rawls's conception of "public reason" asks for a kind of neutrality in the basic rules of democratic discourse. As the Stanford Encyclopedia article puts it, "Proponents of public reason often present the idea as an implication of a particular conception of persons as free and equal."
The presumption is that there will always be profound disagreements with respect to basic values, morals and the best ways to pursue happiness. Living in a democratic society means there is no overriding authority in this regard. It means the government stays out the business of the sacred. It means secular pluralism, especially since our democratic rights are the non-negotiable starting point. Pluralism or secularism is not opposed to religion. In fact, it's supposed to guarantee religious freedom but it certainly is opposed to theocracy or any other form of government that would violate our basic democratic rights. As it says in the first part of the First Amendment to the U.S. Constitution, "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."
Public reason is not the sort of thing that applies to one's private life but rather sets the rules of the debate when we are hammering out the laws and policies under which we must all live. Despite our inevitable disagreements and differences, the proponents of public reason say, our laws can rightly be imposed on us only when they can be justified by ideas and arguments that any reasonable person could at least understand, if not endorse or accept. This sets the rules of evidence and otherwise limits the scope of what can be presented in the court of civic opinion, so to speak. Although we are much less likely to hear complaints about it, the principle of public reason would preclude certain philosophical visions, not just the theological kind. Reasonable philosophers can and often do disagree as to the nature of truth and reality and everything else. Imagine what the reaction would be if someone tried to present our favorite Socratic ideal -- that the unexamined life is not worth living -- as justification for a public policy. That would be quite a trick. Because public reason operates almost entirely within the world of common sense and depends on knowable, checkable, public facts, maybe this principle is a bit too ordinary and dull. Despite this blandness, the principle of public reason certainly has its critics.
The first basic premise, namely democratic rights and liberties, is relatively uncontroversial. But public reason is a particular conception about how to realize or actualize those rights. There are some major differences about what freedom of religion actually means when the rubber meets the road. There is a very noticeable and sustained conflict in U.S. politics involving religion in a wide range of public institutions: schools, hospitals, marriage and even the courts - which are supposed to adjudicate this very conflict. This partisan divide is so wide, I think, that each side sees the other as fundamentally hostile to the fabric of society. The secular pluralists are horrified at the prospects of theocracy and/or global capitalism while the religious and economic conservatives see liberal "equality" as the enemy of freedom itself. It seems the principle of public reason is itself taken as an enemy of freedom by some critics. There is open hostility to it from the religious right, from people who simply don't want to leave their deepest values behind when entering the public forum. They feel it's unfair and maybe even impossible to check these things at the door.
As I see it, democratic pluralism demands a certain kind of neutrality with respect to the various competing visions of the good life, but this neutrality does not extend to neutrality itself. This secular neutrality is itself a value system, a civic morality if you will. In that sense, this neutrality is not supposed to be neutral. Its basic premise is that free and equal citizenship is an historic achievement well worth protecting and so it begins in opposition to undemocratic forms of government. The traditional forms (Monarchy, theocracy) are precluded right from the start. Public reason is meant to protect this democratic achievement; meant to protect the rights of all voices in a pluralistic society - but that doesn't mean that anything goes. In a constitutional democracy some laws would be against the law. "Congress shall make no law respecting an establishment of religion." In that same spirit, public reason doesn't ask us to comply with any single vision of the good life or any particular religion but is itself a kind of civic morality centered around democratic rights. These rights aren't exactly holy things or eternal truths but they are a big freakin' deal in Modern Western culture.