Everything that matters to you is part of an interconnected network that runs through out the country and the rest of the world.
If you fragment the country all of that collapses…
How does a citizen of Texas do business with a citizen in Newyork? By negotiation/navigating all the rules from the states between the two?
What do the two citizens pay each other? Is Texas currency accepted in New York.
No state is a self sufficient entity.