The constitution strictly says that the federal government may only dictate to a state about what it can do when the constitution says they can about things that are prohibited to them. All other powers are reserved for the state and the last time I checked there is nothing in the constitution that says a state can't depart. I don't think that states should leave but it is still a right that they have which makes the union a voluntary union of states that can leave and stay as they please. The civil war did not alter the constitution with new amendments forbidding each state from leaving. It only made the idea of leaving unthinkable because we know their would be a war where any state that wants to leave will be crushed by the US armed forces. This situation is not the path to freedom but to tyranny of the federal government because how can you say each state enjoys a status of being free if the federal government interferes with their own domestic affairs and forbids them from forming their own federation with other states or countries for that matter.