Spanish here, I have family and home in Catalonia. 1) You need to read history to understand the situation. But not the history of the last 100 years, but of the last 1000. Catalonia was never independent, it was part of the Kingdom of Aragon. The kingdom of Aragon and the castle kingdom allied in a dynastic way and created what is known today as Spain. There is no 2) Voting is illegal, it is not illegal to vote but…
I am NOT saying Catalonians are oppressed the way blacks were in the American south or South Africa. Please don’t misunderstand. I’m purposefully using a more extreme example to illustrate that this is a moral, not legal question.
Self-determination is a fundamental human right, by the philosophy of the Enlightenment at least. And this remains true whether or not it happens to be codified in law. If the Spanish constitution blocks reasonable paths to self determination, then the constitution is wrong—morally, not legally, of course.
And why should we support an immoral law? There are good reasons for doing so in fact — preventing anarchy in the pejorative sense — but only if a constructive alternative is provided to fixing the law within the system in a reasonable amount of time. Surely there is a process for modifying or amending the constitution? Spain didn’t try.