The distinction between international law and comparative law is not just conceptual, but is also of practical importance. Thus, the Constitution determines the “law of nations” which – as Justice Ginsburg puts it – “is the core of what we today call international law” to be binding for U.S. courts while foreign law is not. 
This does, however, not necessarily mean that U.S. judges should be blind or ignorant to foreign laws and court decisions. In fact, there are many examples where U.S. Courts have drawn inspiration from a comparative perspective on an issue they had to decide. 
Yet, the question of whether a U.S. Court should look at foreign legal sources or should not has always been (and still is) highly controversial. Opponents basically are concerned (1) that consideration of foreign law might be arbitrary (i.e. only decisions/laws that are in accordance with the own mind set are cited)  and (2) that U.S. judges may not fully get the full picture behind a foreign decision or law due to a lack of (social, historical etc.) background knowledge. 
While the above concerns are definitely valid and should prevent judges from just blindly treating foreign law as binding, I do not see why – especially in today’s interconnected world – foreign legal sources should not get the same level of consideration as other secondary legal sources like law review articles or even legal blogs.  After all, other judges (or legislators) may have already found a good solution, so we do not always have to re-invent the wheel!
 Ruth Bader Ginsburg, My Own Words, 2016.
 Calabresi&Zimdahl, The Supreme Court and Foreign Sources of Law: Two Hundred Years of Practice and the Juvenile Death Penalty Decision, 47 Wm. & Mary L. Rev. 743 (2005).
 see  on page 254 referring to Justice Scalia.
 see  on page 254 referring to Judge Richard Posner.
 see  on page 255.
 for an older post on the Supreme Court and Foreign Law, see here.