This is a systematic and interesting take on the foundations of a liberal (or should I say, libertarian) society. The author places freedom of association first before any other freedoms of the individual per se: the freedom to join and (importantly!), to leave associations of any kind. By doing this he attempts to escape the search for universal common denominators as a basis for society, which must either be trivially poor, or leave important elements of society out because they do not share these beliefs. Kukathas is unconvinced that truly universal values for establishing a foundation for any society, can be found. So instead of a universal set of rights and obligations, he proposes that people be free to associate and dissociate into any (religious, moral etc.) associations with their own restrictions, restrictions that would otherwise not be tolerable under a "common denominator" kind of political organization. You could call it "constitutional pluralism", in a way. He opposes special rights for special groups, which follows logically from the idea that since people should be free to choose the group they want, they can not then argue after the fact that any specific croup should have privileges that other groups don't have. This argument is relevant in discussion of say, aborigine rights whenever they differ from the rights of other groups within a country.
The analysis and oblique approach to liberty proposed here is intriguing. I do have some issues with readability of the text sometimes, the cat is out of the bag pretty soon and the belabored exposition that follows, of reasons, conditions, and bylaws, is a bit tedious at times. Also, the book could have benefited from some more empirical or scenario analysis - to ask not just, why is this desirable, but also, can this work? why would it? why not? But all in all, very worthwhile ideas here, to those who despair between nationalism, special rights groups, and global soup value systems that take a piece from everywhere but work for no one.