>>No, if an EU citizen comes to my US website, that does not grant the EU authority over me no matter what they claim.
You have it backwards. It's not an EU citizen coming to your US website - it's your US website choosing, willingly, to serve EU citizens. You can also choose to not serve them - that's fine. And yes, EU cannot fine you in any way, there's no legal possibility to do that. However, if your operation was detrimental to EU citizens in any way, EU could ask US to cooperate in asking you to stop. Obviously US has the jurisdiction to do something about it, there's no question about that.
To maybe give a different example - if you were selling something that is legal in US but not legal in EU, advertising it, selling it and shipping it to EU customers could still get you in trouble, because at a certain point EU will ask US authorities to stop you from sending illegal products to their territory. You are not breaking US law, but countries do cooperate in this manner. Same would happen in the other direction - if someone was sending drugs that are completely legal in EU over to US, they wouldn't be braking EU law - but US definitely and absolutely would ask local authorities to find you and politely ask you to stop. Does that mean US suddenly has jurisdiction in the EU? No - but EU would most likely comply with such a request as a matter of international cooperation.
And yes, the same request sent from North Korea or from China would likely be ignored - that boils down to what I said earlier about negotiating power and international respect. EU countries are very likely to comply with requests like these coming from US, and EU can and does request things from US. It has nothing to do with the issue of jurisdiction that you are so very keen on.
>> I don't have to give a damn about EU law while operating my US business in the US.
Again, if your US business does serve EU customers, then you kind of have to give a damn. Just like an EU business has to give a damn about US laws when doing business with US customers. It's really not a difficult concept to grasp.