The UK -- and many other countries -- assert that their laws do bind people outside their borders, regardless of the absurdity (in most cases) of attempting to enforce that law elsewhere.
I think it's important to fight these sort of things even in cases where they can't actually enforce it. For one thing, say one of the site operators in question have a need or desire to visit the UK at some point in the future, but can't, because there's some sort of legal judgment against them because of this. That would be a shitty situation.
On top of that, ignoring these sorts of things also ignores possible efforts by the UK to convince other governments (like the US) to adopt similar laws, or at least agree to some level of extra-territorial enforcement. Fighting these cases sends a signal to everyone involved. You mention the UK acting like a petulant bully: yes, sometimes a good way to counteract a bully is to ignore them, but other times it's good to fight back, even when the current bullying wouldn't be effective... because future kinds of bullying might be.
"The UK -- and many other countries -- assert that their laws do bind people outside their borders…"
I'm aware of that, it's become an increasing trend over the past 40 or so years as diplomatic norms have broken down, changed or become more disrespected. If it continues we'll see even more tit for tat reprisals as respect for international law and authority continues to break down (we're now 80 years on from WWII and the world has almost forgotten lessons learned and the international order that arose from that conflict).
"…have a need or desire to visit the UK at some point in the future, but can't, because there's some sort of legal judgment against them because of this."
I remember a time when my passport was stamped in big purple letters "Not Valid for XYZ" country for reasons like that (I could not legally leave the county if that was my destination).
Matters would likely come to a head if say US passports were stamped "Not Valid for the UK". Moreover, it's incumbent on a country to protect its citizens who have done nothing wrong by their laws—hence a country should so warn its citizens beforehand, and stamping passports with large signs is very effective.
This is all part of a much bigger issue too big to address here. It's why I believe it's going to get much worse before it gets better. As I said elsewhere, I believe that with the increase in political and cultural differences brought about by rising nationalism we will see an increase in geoblocking everywhere. I find the trends shocking but there's stuff-all I can do about them.
Edit: I must emphasize that whilst I'm defending the right of law abiding US citizens against action by other governments, I'm not defending the US Government per se (some of it's actions of late I consider alarming). Again, these are separate issues.
I think it's important to fight these sort of things even in cases where they can't actually enforce it. For one thing, say one of the site operators in question have a need or desire to visit the UK at some point in the future, but can't, because there's some sort of legal judgment against them because of this. That would be a shitty situation.
On top of that, ignoring these sorts of things also ignores possible efforts by the UK to convince other governments (like the US) to adopt similar laws, or at least agree to some level of extra-territorial enforcement. Fighting these cases sends a signal to everyone involved. You mention the UK acting like a petulant bully: yes, sometimes a good way to counteract a bully is to ignore them, but other times it's good to fight back, even when the current bullying wouldn't be effective... because future kinds of bullying might be.