Opponents of secession say secession is wrong if some people in the population don't want it and say they will be worse off. The American revolutionaries disagreed and seceded anyway.
Why decentralize? One: small polities allow for more choice and opportunities for exit. Two: small is better for minorities when democracy fails. Three: small polities limit the power of aggressors.
For more than a century, the union of the Kingdom of Poland and the Grand Duchy of Lithuania made possible one of the most liberal societies to date. The commonwealth left much to emulate.
All too often, people equate their nationality with a particular state. Yet, as Mises noted, nationality does not depend at all upon a formal entity tied to a government.
So, if we're going to talk about secession, then, it's also important to explicitly address the issue of "what is the correct size of states." Is smaller better?
In this politicized age, being an American means little more than being subject to the federal government. Yet, as Rothbard noted, we are not "the government," but rather people who are part of like communities, which we should celebrate.