> The US government is not free to use frivolous sanctions to indirectly make payment processors stop serving a foreigner.
You may regard them as such, but they are not in any sense frivolous. It is the law that if-x-then-y, it's not a discretionary item that one interprets. And to be clear, these are not "indirectly" making payment processors stop serving the person, it is very clearly direct and you do not, as a company, have a choice in the matter.