Logic says that that each state must be able to leave the union or the contract is not voluntary, agreement to the contract was and or is coerced or forced. This invalidates any contract by definition a contract is a voluntary meeting of the minds.

The idea that a morally bankrupt concept Might Makes Right is used to say the issue was decided by an unconstitutional war is ludicrous.

Since the use of violence (in the war between the states) to stop states from leaving voluntarily we now know that there is no constitution, there is no union, there is just the force of the federal government (an entity created to carry out the wishes of the several states). If the several states no longer exist as a party to an agreement by the act of secession which nullifies the contract, the federal government ceases to exist as it is the offspring of the agreement. No agreement no federation no government, completely logical consequence of the voiding of the contract.

The above idea is why there is always vehement opposition to the idea of nullification or secession. It calls in to question the existence of the federal government.