Let the Catalans Say Adios to Spain

A large region of Spain called Catalonia has announced October 1 as the date of a binding referendum on its independence from Spain. This is the culmination of eight years of independence activism, regional elections, and public consultation. The Spanish government says the referendum is illegal; the Spanish Constitution declares Spain to be "indivisible." If the referendum vote succeeds, should Spain allow Catalonia to secede? And if the Spanish government forbids it, how should other governments respond?