This concise (5 short chapters), very well written, and unusually well argued book is devoted to addressing the major question: "what are the principled reasons why the state should exempt religious claims of conscience from the burden of its laws?" While the focus of this book is on the legal status of religious claims to receive preferential treatment from the state, Leiter's arguments have significant implications for the general deference that religious claims receive in American life (and in that of many other democracies). Leiter starts with the basics; why should religious claims be tolerated? In his first chapter, he grounds "principled toleration" - the tolerance of ideas and some actions that a majority would find objectionable - in both deontological and utilitarian traditions. This is a thoughtful, parallel application of Rawls' Original Position and ensuing arguments, and Mill's utilitarianism. Through both the Rawlsian and Millian analyses, Leiter establishes that religion deserves principled toleration. A key point, however, is that these chains of reasoning indicate that liberty of conscience in general deserves principled toleration, religion here appears only as a sub-species of claims of conscience. After establishing that religious claims deserve principled toleration, subject to important side-constraints, Leiter moves on to the question of whether there is anything distinctive about religion that would demand preferential treatment compared to other claims of liberty of conscience.
This further discussion demands an understanding of what constitutes religion. In his 2nd and very interesting chapter, Leiter suggests a thoughtful definition of religion. Religion has 3 primary characteristics; it makes categorical demands for actions, it is insulated from evidence, and it offers existential consolation. The discussion of these points is particularly interesting. Leiter explicitly discusses one of the major "political religions" of the 20th century, Marxism, as a contrasting phenomenon. Since Marxism made claims to be a scientific theory, it is formally (though not necessarily in practice) susceptible to evidence. Leiter's definition could, however, incorporate some phenomena, such as versions of fascism and racism, not ordinarily thought of as religious in nature. I don't think this is actually a weakness as it points the way for Leiter's concepts to be used as the basis for a larger typology of ideological phenomena.
With a characterization of religion in hand, Leiter turns to examining whether the distinctive features of religion demand preferential legal treatment. In the 3rd chapter, Leiter returns to the basic Rawlsian and Millian arguments to assess the potential privileged status of religious claims. Leiter finds that neither the Rawlsian nor the Millian bases for liberty of conscience demand preferential treatment for religious claims. These claims deserve the same treatment as other claims of conscience. If anything, and based on a thorough Millian analysis, we should be attentive to the categorical nature of religious demands for action and its insulation from evidence, and be cautious about the tendency of religion to breach crucial side-constraints governing exercise of rights. In a related argument in the 4th chapter, Leiter examines arguments that religion deserves something more than toleration, it deserves "respect." I suspect this chapter was included as a response to recent work of his University of Chicago colleague Martha Nussbaum. Leiter decomposes respect into 2 categories, recognition respect and appraisal respect. As he shows, the former is really equivalent to principled toleration and provides no basis for extending religious claims preferential treatment. Appraisal respect, however, attributes distinctively meritorious features to the object of respect and the question that logically follows is whether religion possesses such attributes. Leiter reasonably argues not - the insulation of religion from evidence counts strongly against appraisal respect for religion.
Leiter takes up the issue of how legal systems should treat religious claims of conscience in the 5th and final chapter, another detailed and thoughtful analysis. Given that religious claims can't be distinguished from other claims of conscience, one option is to treat all claims of conscience as we presently treat religious claims. Leiter dismisses this idea on practical and theoretical grounds, carried to logical but hardly implausible ends, it undermines the idea of law itself. Leiter favors a nuanced No Exemptions policy; claims of conscience do not deserve exemption from generally applicable laws with neutral objectives. He has very good discussions of the implications of this approach, including some concrete examples of how it could/should be implemented. Leiter also has a thoughtful discussion of the relationship between religious establishment and principled toleration.
Overall, Leiter's sustained argument is very successful. He is likely to receive criticism primarily from those who reject the foundations of his argument - his Rawlsian and Millian bases, and in particular, his categorization of religion as invulnerable to evidence. Religious believers, feeling themselves in possession of unique truths, will certainly reject this conclusion. While Leiter is focused on legal issues, his arguments have larger implications. If religion doesn't deserve preferential legal status with respect to exemptions from generally applicable laws, than what of the other aspects of the deference it receives in American life? Why should churches automatically receive tax-exempt status? Why should religious belief (or to be more accurate, profession of religious belief) be equated with moral seriousness?