Opinio Juris has an interesting post on Justice Kennedy and the reference to international law by the Supreme Court. I totally agree on the point concerning the US and international law. I also agree on the lack of meaning of the 'world-is-flat' metaphor.
The final point expresses skepticism as to the desirability of judicial reference to international material in the interpretation of the Constitution:
"What is "beginning" is aggressive judicial invocation of international law (even international law that the other branches have rejected) to interpret the U.S. Constitution. This is new stuff, and I don't think (based on his own use of it in Lawrence and Roper) that Justice Kennedy himself has come up with an explanation of why it is so important to cite international treaties when interpreting the Constitution. No justice has offered a particularly impressive defense of this practice (see discussion of Ginsburg here and Breyer here). It's too bad that the Justice can't do better than simply telling us that the "world is flat"."
I would like to moderate this skepticism by saying that the both the decisions in Lawrence and Roper are to be welcome as a progress. From the point of view of an outcome based type of constitutional philosphy, I would say that these decisions are un-objectionable.
Of course, the problem here is the procedure. I think I can give a pragmatic answer to that. I remember asking Justice Kennedy, after a public speech at NYU, what lies behind his conviction that external sources to the US system can improve the interpretation of the US Constitution. His answer relied on his pluri-annual experience as a visitor at the European Court of Human Rights, in Strasbourg. As you know, the Strasbourg Court hears cases coming from more than 40 different judicial systems in Europe. It does so by consulting with other National and International Courts. It does so under the constant risk of unduly impinging on the constitutional balance of other legal systems. Yet, I guess, the external observer can see a virtuos circle in this kind of procedure that takes open and engaging debate with other leading institutions as an advantage rather than a burden.
My guess is that Justice Kennedy sees this open confrontation as a virtue too. His message is: other jurisdictions are serious about international law and they are progressing fast under this stimuli. If the Supreme Court wishes to continue to be a leading source of constitutional debates, than it has to engage itself in constitutional conversations. Otherwise, it will be regarded as a narrow minded, not-very-authoritative, court. If it does not do so, while other leading jurisdictions are, then it will simply lose the place it used to have in the "global constitutional market."
This explanation, however, is not sufficient as far as American Constitutional Law is concerned. The Supreme Court competitiveness on the global constitutional market is not enough to justify the bending of the Constitution itself. But this is another matter, and I leave this argument to federal constitutional justices.