It is not "certainly" a basic right. Some countries accept it, others do not.
As for the cultural, language and historical I see absolutely no basis for this referendum. Cultural wise I have never, ever, see the slightless difference between catalonians and people for the rest of Spain. What will be the difference between someone that lives in Tarragona and someone from Valencia? Of course it's all a smooth change, and the farther away you go the more small changes you get, but I have seen much deeper differences between people living in cities vs rural areas (even when they are close to each other).
In any case, these differences are (to me) smaller than the differences between a New Yorker and a Texan.
Historically Catalonia has never been a separate, independent country, and you have to go pretty far away to get a substantially different Spain to what you have today.
Catalonia has a different language, that roughly 60% of their inhabitants do not speak, and that is shared by some of the inhabitants of the spanish states (Comunidad Valenciana and Balears).
If your point is that Catalonia people should be allowed to secede because they have a differenciate culture / language (let's ignore for a second all the catalans that do not speak catalan), why don't they call to vote in catalonia, comunidad valenciana and balears, all together? Because they will very clearly lose the vote.
In polls there are a huge number of catalans descendants from andalusia n "inmigrants" that are also for the independence. Why is it so? Because the reason argued again and again during years has been only one: taxes. Not "culture".
BTW, they wanted the Estatut to pass (it passed in congress), but you needed more than 1/2 the votes, you needed 2/3. If the Estatut had nothing against the Constitution, it will be law by now.