Bear in mind that this has no bearing on the point under discussion.

It definitely does; my point is that sanctions aren't very granular (essentially like surgery with a spade), and make life miserable for a whole bunch of people and companies that you didn't want to sanction. Of course, you inflict a lot of damage to yourself as well, as we're experiencing in Europe currently.

But the whole bureaucratic issues are not to be underestimated. At some point, the US eased the sanctions on Iran a bit (under Obama I think), and my former colleague tells me that quite a few European companies were up for doing business with Iran (related to your regular old passenger cars in that case). At some point the sanctions got reinstated, and several German and French companies were threatened with sanctions if not outright sanctioned. My former employer (before my time there) had 2 projects worth ~$5M (of 2010s US dollars, not the monopoly money I earn now) total with some of these companies, and both were axed, even though the company itself had absolutely nothing to do with Iran. They got some compensation, but like not even 10%. Apparently, the whole sanctions thing is considered a "special case" in contracts.

It does, actually. Secondary sanctions are an impediment to free trade and frequently argued to contravene against international law as a result. You could take it up at the WTO if the US didn't just destroy it a couple years ago.