So you think any political entity, regardless of where it is located and how it is incorporated into a larger entity should just have a carte blanche right to secede or separate ?
As much as I sometimes wish Texas would secede (LOL) viewing any mere “vote” for separation/secession as a practical means to arrange or organize political entities is somewhat ludicrous!
And why only a “supermajority” ? Why not just a majority? or why not 3/5ths? Where do you draw the line? Should Bavaria now get to separate from Germany? Provence from France?
As I noted in the original question, Spain has been a geographically/politically cohesive nation since 1492. This is not an example of Yugoslavia cobbled together in the last 70 years or various middle east nations whose lines were drawn arbitrarily by western powers 100 years ago.