There's been some buzz in the last decades over whether or not Pima County will split from the state of Arizona. The big question of course is should they? My answer is this: if the people of Pima County wish to secede from the state of Arizona, they have every right to. Done.
This issue kind of ties into the issue of secession from the United States, and whether or not it is legal or correct to do. My answer is exactly the same: if the people of a particular state desire to leave the union, they should be allowed to. It may not be what we want, but if it is the will of the citizens then it should be allowed.