It is a dilemma. Clearly better answerable by people far above my pay grade. I do think any technology can be purchased or stolen without too much trouble, and the US might not even know about it for a while. And there is no reason to assume that companies headquartered in the US will respect US government wishes or actively patrol regulations. Marx was probably right about the rope. But I suspect the US government has its own ways of determining sales and transfers under the table, even if politically the government can't or won't do anything about it. Maybe best to keep and improve sanctions for political reasons. Violations of sanctions, when brought to light, may stimulate more response from the general public and force some political action on companies as well as on the underground market.