Piracy has flourished in the crucial shipping lanes off the coast of Somalia partly due to a treaty that the U.S. has not ratified yet -- but which is often described as "customary international law" binding on all nations. Partly as a result of the LOST Treaty, billions of dollars worth of cargo, and human lives, have been lost due to piracy. Harold Koh, nominated by Obama to be the State Department's chief lawyer, argues that "customary international law" like LOST is binding on the U.S., even when it is reflected in treaties that the U.S. has refused to sign. (European human-rights conventions and an indecisive White House also play a big role in thwarting action against the pirates).
That's just one reason U.S. policymakers should think twice before following vague "international norms."
Since customary international law is vague, liberal lawyers invariably use that ambiguity to claim that it dictates a host of controversial requirements that few countries would voluntarily adopt on their own, like banning Mother's Day as sexist, and mandating quota-based affirmative action. For example, the CEDAW equal-rights treaty has been construed by an international committee as requiring "redistribution of wealth," "affirmative action," "gender studies" in academia, government-sponsored "access to rapid and easy abortion," "comparable worth," and "the application of quotas and numerical goals and measurable targets aimed at increasing women's political participation.”
But they only adopt expansive interpretations of international law when it is ideologically convenient. When looking to foreign court rulings or international law would actually result in a conservative outcome, they cheerfully ignore international law or pretend it doesn't exist. A classic example of that is Justice Ruth Bader Ginsburg, who claims that the Supreme Court should pay more attention to foreign court rulings, but ignores those rulings when they contradict her political preferences, even in those atypical cases where foreign court rulings actually deserve to be given careful consideration (like when they are interpreting a commercial treaty that also applies in the U.S.).
People who claim to care about foreign court rulings or "international law" cheerfully ignore them when they result in "conservative" outcomes, like limiting taxation or punitive damages against businesses.