National culture is a meme. Ours and most other country's too. Nation states fabricate a fake, lame, common denominator base culture for more effective control of the population. They do everything they can to deracinate the individual and prevent him from having real bonds to its close and extended family and his REAL, ORGANIC local culture (village, city, small geographical area, ...) and ethno-racial in-group preference, and after they do so the individual, still feeling the need to belong to a group, identifies himself with his nationality and the manufactured national culture the state has created for him.
This is why people will turn their backs on their relatives, their parents, their children, their lifelong friends if they disagree in things like politics or culture and will willingly serve their government and even volunteer to kill and get killed in war like the good little brainwashed slave he is.
Notice how the shittier and less developed a country is, the more fervently nationalistic its people are. And even inside countries, the more developed and prosperous parts will always be the ones that have their own strong identity and culture and reject the national one. (In our case, being Spain the multicultural country it has been since its inception, this is far more blatantly obvious)
