That's a strange argument. Should the other member states of the EU have gotten to vote on Brexit?
So while only UK citizens got to vote on brexit the legal possibility to exit the union was actually approved by all the EU members. If there was an article in the spanish constitution that allowed for a region to secede under certain conditions we wouldn't be having this discussion.
Furthermore the UK always remained a sovereign state, with its own currency, army etc... It's hardly comparable to Catalunya. The scottish referendum would be a better comparison.
[1] https://en.wikipedia.org/wiki/Article_50_of_the_Treaty_on_Eu...
Authority emanates from people, not from papers.
A state constitution must offer a framework which is interesting for all of its peoples and territories: if big groups of people do not see the point of it, it looses its validity.
I hope the Catalans that voted to leave have really good reasons to do it, because if the situation isn't defused somehow, there are some tough times ahead.
It is not clear we are in a modern era.
An EU vote on Brexit would make no sense, as one or more of the countries would have to withdraw from NATO in order for a war to occur. The unlikelihood of war among NATO members is probably one of the reasons why exit procedures exist in the first place--the other notable reason being that some countries never would have joined in the first place, if they thought they would have to fight their way out.
Spain, on the other hand, has apparently never been shy about fighting Spaniards. It might be appropriate for Spain to hold a vote, but only to show Catalonia what it may be up against, and a "no" vote gives the national government a mandate to be brutal. They can, of course, be just as brutal after a "yes" vote, but the propaganda budget would be higher.
No, it might be that, if a war occurred either NATO would cease to exist as a credible alliance or one or more countries would be expelled from it and find themselves at war with it, but certainly withdrawal from NATO isn't a necessary precondition for war.
There are many examples of self determination in 20th and 21st century, and normally only region/area that wants to become independent votes. Most recent example is independence referendum in Scotland. Entire UK did not vote, only Scotland voted.
It's more like "90% of the people who thought the referendum was legitimate are in favor of independence". There's obviously a big selection bias.
As for the question of whether the referendum was legitimate or not, the problem in my opinion is how can you consider a referendum democratic if only a tiny portion of the country's population gets to take the decision? Catalunia becoming independent would have consequences throughout the country, shouldn't everybody get to vote?
And if not, where do you draw the line? Paris and its region generate about 1/6th of the total GDP of France, what if Parisians decided to declare independence? What about the Lega Nord in Italy? And let's not even talk about the historical economic divide between eastern/western Germany or the variations of GDP between states in the USA.
What if all the rich people in Japan decided to all move to an inhabited island and declare independence with 100% of the vote? Would that be legitimate?