I have no particular view on the outcome of this, but the fact that upwards of half a million protestors turned out in Barcelona suggests that it’s an important issue.
My understanding is that the polls were not universal, but only ran in the Catalonia areas with strong support for independence. And there was no vote security and verification, in fact, people were encouraged to vote multiple times in the same referendum.
So the referendum could not be construed as legal.
I think the real problem is that Spain have consistently blocked a peaceful referendum. I don't believe Catalonia would vote to leave in a fair vote, but I do feel that the repressive actions of the Kingdom of Spain on this matter are the kind of thing that could justify declaring independence unilaterally.
Denying people a right that's commonly understood to be fundamental to international law and then using violence to enforce it is repression in my book. Spain has consistently escalated tensions rather than offering a path to a real democratic decision. They're going to have to accept the repercussions of that decision.
Most importantly: the referendum is illegal even by the autonomic law of Catalonia. They should have had 2/3 of the chamber to push it, and they did it with less than half (48% IRCC).
It was not as much as it seemed: "That woman who had all her fingers broken. She hadn’t. That six-year-old boy, paralysed by police brutality? It didn’t happen. Serious injuries on the day: just two." https://www.theguardian.com/world/2017/oct/08/catalonia-demo...
Even if Catalonia somehow manages to enforce its declaration, the economic consequences will be so devastating that they will reverse course in due time.
If anything, economic troubles reinforce the determination.
Once people take independence as a question of pride, they're extremelly reluctant of considering selling their independence for money.
Anyway, I think the calculus is unique in this case. We are already seeing major companies move their headquarters out of Catalonia. Catalonia's independence would mean disruption of access to EU common market benefits and Schengen. Also they couldn't stop smaller provinces from voting to rejoin Spain.
Not sufficient to win maybe, but definitely to mandate some sort of peacekeepers.