Peter Schuck's Diversity in America makes the most important contribution in recent years to the clarification of a mostly muddled topic. Whether you agree or disagree with his conclusions (I do some of both), it is impossible to come away without a more sophisticated intellectual framework and a far richer understanding of the stakes.
Galston, William A.
"Liberal Government, Civil Society, and the Rule of Law,"
Yale Law & Policy Review:
1, Article 4.
Available at: http://digitalcommons.law.yale.edu/ylpr/vol23/iss1/4