Circular reasoning.
In practice, if an oath-bound group of men decides to separate from the union, they're guilty of insurrection, suppression of which is explicitly authorized by the Constitution. If a state officer "shall be bound" by his oath to support the Constitution, and as such he agrees to the superiority of the Federal to the state government. That's the whole point of the government defined by the Constitution! And by pulling out of the union... he's breaking his oath.
I believe in the Constitution 100%. However, the federal government has usurped powers from the states that were never relinquished. As a matter of fact, the Constitution clarifies that states retain those rights in the 10th amendment.
Why do you think that prohibition required a constitutional amendment, but anti-drug laws do not? The federal government never had the power to force states to obey these laws, so they have found ways to stretch and manipulate the original intent of the Constitution to invent powers they never had.
Since the passage of the 17th amendment, the states unfortunately no longer have representation in Congress to control over-reaching federal powers as the founding fathers intended.
The contract was breached by the federal government a long time ago. Most states just put up with the federal government's “illegal” abuse, but they are starting to see the light. We want a divorce.
You can call secession a breach of contract if you want, but that doesn't make it wrong, any more than divorce is an unfortunate, although necessary part of life.
The People are not required to take an oath to the Constitution. We are a free people. We have the right to change our government to serve our needs. To say otherwise is to be contrary to the definition of liberty. The founding fathers knew this and it was anticipated. It's why we have the 2nd Amendment.