The supremes are wrong, just as they are wrong on other rulings. There is nothing in the constitution that prevents states from leaving the Union, if you think there is point out the article or the amendment that states this. You trust the same court that said Dred Scott was property and could be bought and sold and found a so called "right to privacy" that makes killing unborn children legal? That Supreme court?
Any time you join something, you have the right to unjoin it. The civil war started because the Union simply didn't want the southern states to leave. Lincoln didn't give a rat's behind about slavery, he wanted to send the blacks back to Africa. He simply didn't want the Union to fall apart on his watch, so he ended up killing 600,000 or so Americans to accomplish that end and called the Southerners "rebels" when, in truth, there was or rebellion. Secession is legal and just.
Read the constitution, all of it, including the preamble. Tell me what you think the founders meant when they said that men have the right to choose their own form of government and to throw the old one out if it becomes too onerous to bear. Seceding is exactly that, choosing the form of government one wants.