During lawschool, I took my international law course from a man who had help written a constitution and whose brother is current president of Malawi. All of the source material he tought showed no example of a true international law outside of treaties, yet when I suggested as much I was told I was wrong (ha!). Such was his devotion to the U.N. and transnational control from a self-appointed elite, mostly in an effort to tie down the collosus. A pox to it all.

My favorite argument was that the Constitution is functionally just another treaty, and therefore deprecated by every subsequent treating signed. He criticized those who disagreed as “monists.”

“As for professors of International Law, I assume that most got into the field not to study it so much as to promote it.”

Of course.

Back when I was studying International Law, two major methods were described for creating it “silence is refusal” (as in treaties) and “silence is consent” (as in, customs & norms). [1] Another set I heard of as sources of international law are treaties, international court decisions, customs, and scholarship.

I agree with you on previous Catholic and Muslim international laws. The professors take when I suggested that was “no one who knows anything about international law could possibly say that.” So we had similar experiences

To me, this comes down to the nature of our Republic.

Every argument that international law has any effect comes from Article I Section I, granting Congress the power “To define and punish Piracies and Felonies committed on the high Seas, and Offences against the Law of Nations.” Thus while Congress is certainly free to “punish… Offenses against the Law of Nations”
this is in the context of the facts that

“All legislative Powers herein granted shall be vested in a Congress of the United States” … “The executive Power shall be vested in a President of the United States of America.” and “The judicial Power of the United States shall be vested in one supreme Court, and in such inferior Courts as the Congress may from time to time ordain and establish.”

And, of course, “The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”

The “Law of Nations” cannot legislate, because only the Congress can legislate. The “Law of Nations” cannot execute, because only the Congress can execute. The “Law of Nations” cannot judge, because only the Supreme Court (and such inferior courts) can judge. And everything that those branches can't do can only be done by the States.

[1] http://www.tdaxp.com/archive/2005/09/20/international-law-and-boydian-instructional-psychology.html

As for professors of International Law, I assume that most got into the field not to study it so much as to promote it.