What does the 1000 year history have to do with anything? If the people want independence now, that's all that matters.
What would happen if California were to separate from the US? Who would afford their army? What about billions invested by the whole of US in the industries there?
By your logic I may just reply that "if the people want independence now - then all that matters if I have enough military power to keep them in the saddle". Because the laws are changeable.
That's pretty much how most declarations of independence have worked historically. But even if you have enough military power, how much blood are you willing to shed if a full blown civil war breaks out? If there are civilian deaths, it's likely that there would be condemnation and support for the separatists from the international community. What matters is how badly people want their independence and how far they are willing to go for it.
Give it up and someone else will happily take it: what about deregulated toxic disposal at the state level? what about coca leaf production in deserted areas? arms production with no oversight?
Well, here we are.
I would say they got what they paid for. Satellites and computers have been delivered. Investment paid off.
For one thing it would destroy half the countries in the world, and most of them aren't highly developed nations that can vaguely cope with it.
For another, how do you set limits, why is Catalonia special but any random town or city isn't?
There's also the point that (probably) irreparably destroying countries based on slim margins and changing whims probably isn't smart.
Now that's not to say I wouldn't support a (legal) referendum in Catalonia, but you do need to treat it with some nuance.