The problem here is that all the inheritants of the Franco dictatorship and their mentailty are still in the power, thanks to the Spanish transition in which the Dictator passed the power to the King. Then promoted a bi-party politics where the minorities would never be able to change anything.
It is not fair and Catalonia is fighting (again) to change it.
After Franco, Spain has been governed for 6 years by centrists, 21 years by socialists, and 14 years by the PP.
The fantasy of "the Transición didn't take the francoists off the power" would need the likes of Felipe Gonzalez be "mentally francoist". It's no more than a feel-good fantasy.
The fact that you need to convince the majority to change something, while individuals are constitutionally protected, is really how democracies work. If anything, nationalist minorities have wielded much more power in the Spanish Congress than other minorities with more voters, due to quirks of our electoral law.
It is not fair and Catalonia is fighting (again) to change it.