[pqs]

My mother tongue is Catalan, which is as Spanish as Castilian itself.

The problem is that both Catalan and Spanish nationalists like the idea to identify Castilian with Spanish. The Catalan separatists like that because it is the proof they are not Spaniards, since Catalan is not from Spain, and the Spanish nationalists like it because it puts the other Spanish language in a second level, something they love.