If secession is illegal, then a) revolution is the only alternative to redress wrongs and b)states are indeed subservient to the federal government, contrary to the Constitution.
Wasn't that "settled," for worse, by the Civil War?
Most importantly, the principle of local control, or "subsidiarity," is part of the natural law. A confederation of states, held together loosely by a federal government (the pre-Civil War United States), would be more in keeping with this principle.