I do not think that is important whether federal law permits states to secede from the Union. Surely, British law did not permit the American colonies to unilaterally decide to become independent. It was clearly illegal under British law. Yet, the Patriots relied upon the superior, natural rights of man, citing their God-given rights and declaring that “whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it...” Who would expect the United States government, including its Supreme Court, to declare secession legal? I would presume the very opposite.
The Constitution is silent on the subject of secession. Meaning it is a right reserved for the state(s). Read Mr. Williams article it is well worth it.
You’re exactly right. It really doesn’t matter whether secession is “legal”, because it is always permitted by a higher law than the laws of men. The only thing that really matters is whether the people have the resolve and strength to exercise their rights in the face of opposition from the government.