-Most of us are governed by several levels of administration: local, regional, national, European, global. No referendum is going to change this or make us suddenly "free."
-Most of us have several identities, and if one believes he or she has only one identity, chances are that he or she shares the house, the street or the city with people that have other identities. There are no territories in Europe with one single "us."
Sovereingties are overlapping and shared.
This is the reality of Europe in the XXI Century and our democracy should adapt to it, not try to create another reality.
The nation-state in Europe in the XXI century is obsolete, as brilliantly pointed out by Joschka Fischer in a recent article (did the Scottish Green read it?). Identities are social issues, and those that naively wave them should be aware of the unintended consequences: the path to hell is paved with good intentions.
In Catalonia, if a referendum with a yes victory for independence was followed by a negotiation, the outcome in the euro zone would be the same as the outcome of a referendum, much less divisive, that rubber stamped an ex ante broad agreement. If we consider the possibility of unilaterally exiting the euro zone, that is uncertainty and probably financial ruin of the greatest scale.
As argued earlier here, the possibility that a tight majority in a relatively rich region may alter the remaining borders of a euro zone country is the ultimate commitment problem. In our institutional architecture, we need innovation, flexibility, FOCJs (functional, overlapping and competing jurisdictions), and be aware that with globalization, states and markets should fit as much as possible in size and fluidity.
A referendum to endorse a broad agreement among a large majority of citizens that share common values is a better way to democratically decide things than a secession referendum. This would be as consistent as the proposed consultation in Catalonia with the existing broad support for some kind of decision or consultation, and it would fit much better with the current Spanish and European legal framework. It would be a way to decide on institutional architecture that fits with the reality of bodies that are for good reasons evolving towards federalism (Spain and Europe).