No one has ever argued that they do not have that power and certainly not I but you have yet to show me the Article, phrase, or word, in the Constitution which would prohibit a sovereign state from leaving. When you do that you have won the argument until you do so you are just making lots of noise and throwing stuff against the wall hoping something will stick.
Can a state be expelled from the Union against its will? In other words, can we get together and boot those liberal a-holes in Massachusetts and their whole miserable Kennedy clan right out of the U.S. and never have to worry about them ever again. Wouldn't that be permitted?