Okay, so why are people so against this? America is a far too big country already, especially for the inefficient form of government you have, it's a far too powerful country as well. Dividing it up a bit would make it both easier for people in the country to be heard, to be able to live as they wanted, and it would serve to calm down a huge portion of the world, since we wouldn't have to worry about America snapping anymore and taking out half the world with nuclear weapons.
Just let them leave if they want to, what's the big deal? If they want to stay in America, great (or not), if they want to leave, so what?