US question: Would you approve of your state seceding from the Union, declaring independence from the United States? I think California, Oregon, and Washington would, and probably Colorado too.
If you want to gain independence, you have to fight the federal government's monopoly on violence. At its core, that's how all law is backed up. Two things you need to be a country. First, the ability to backup your independence with force. Second, the acknowledgement of the international community and their willingness to sign treaties with you. Sealand doesn't have any issues defending their "independence", but no one has signed a treaty with them for instance.
No but there's no law against expelling a state from the union. Kind of a reverse secession if you can piss trump off enough for him to actually do it (no law saying that only Congress can expel them, so it would go to the courts).
To take this in a different direction, legal or not (considering the "higher power" generally gets to define what is and isn't legal and might do so for its own benefit rather than in the best interest of everyone, if there even is such a thing), how can it be determined if a subset of a power structure breaking away from that power structure is a good thing or bad thing? What arguments other than "we'll use force" are there to support a region needing to remain under the thumb of a power they no longer wish to serve?