I'm familiar with the so-called ethics/law divide, where some acts may be lawful but unethical and other acts ethical but unlawful. This question is not about this.
I'm also familiar with professional Codes of Ethics that gain "legal" force by virtue of contract law and/or incorporation into professional regulatory statutes, but generally only apply to certified or licensed professionals (e.g. non-physicians do not incur liability by behaving in ways that are inconsistent with contemporary medical ethics but are otherwise lawful). This question is not about this either.
Has US law ever imposed a general duty on the general public to behave ethically? Restated, has a court ever imposed liability on a private citizen (holding no professional licensure or certification, holding no public office, etc.) for behavior that did not violate any specific provision of criminal or civil law, but rather transgressed either normative community ethics or the court's view as to what such ethics ought to be?
I used to think that it would be absurd for there to be "purely ethical" liability, but I found this article by an attorney in Arizona, who seems to be primarily talking about professional ethics (not general citizen ethics), but states that a court could theoretically punish on the basis of transgressing an ethical rule that has broad community acceptance but that had not been formally accepted by or imposed on the defendant by specific legal process.
If asking about the United States in general is too broad, we can limit it to the state of New York.