Most satellite systems allow countries to block access. The first tier is refusing to sell to locals/local billing addresses (which is ALSO imposed by sanctions, e.g. due to USA, satcom vendors with any US connection don't sell to Iran/NK); the second tier is allowing countries to ban operation within their borders. There are tricks (what actually matters to the satellite is your exact delay, so there's a range of spots which look the "same", and you can spoof GPS or fake it in the firmware...), but that's more applicable to fixed C/Ku VSAT than it is to portable systems like Starlink.
I'd love it if the US gave Musk the diplomatic/military cover to make Starlink available globally, but we might end up with issues (ITU or jamming/military) if that happened. Might still be worth it though.
> what actually matters to the satellite is your exact delay, so there's a range of spots which look the "same"
That's potentially true for GEO systems. It's not at all true for LEO/MEO systems, where ⓐ that "range of spots" is rapidly moving over the surface of Earth as the satellite does, ⓑ you have AOS/LOS when the satellite crosses the horizon, and ⓒ you can get enormously improved bandwidth for a given power budget by using highly directional antennas on the satellite as well as the groundstation. Starlink is LEO.
I'd love it if the US gave Musk the diplomatic/military cover to make Starlink available globally, but we might end up with issues (ITU or jamming/military) if that happened. Might still be worth it though.