[Brass Lamp]

With the exception of the original 13 states, the individual states decided nothing. They were admitted and only after the existing states said that they could joing. Why should leaving be any different?

Law isn't symmetrical nor does it rhyme like poetry. The powers of government are derived from the rights of individuals. They are comparable across their differing scales. If you want to know what powers a government has, look first to what powers its constituent citizens enjoy and scale that up. Can you imagine, as a private person, joining an organization which initially requires their consent to joint, but which then also requires their consent to quit? The Mafia, perhaps?

[Brass Lamp]

requires their consent to joint,

Uh, wrong argument. "join", should be.

[DoodleDawg]

Can you imagine, as a private person, joining an organization which initially requires their consent to joint, but which then also requires their consent to quit?

You have just described most business contracts that I'm aware of. Ending the agreement almost always requires the agreement of both sides, absent a complete violation of the contract by one side.