I think that it is unfortunate that this seems to be the consensus among a lot of people. While there is clearly nationalism in both sides, we can't generalize

I think that it is unfortunate that this seems to be the consensus among a lot of people. While there is clearly nationalism in both sides, we can't generalize and state that both pro and against independence are basically nationalist movements. That's unfair, that is simply not true. Catalan independence movement is highly diverse, with people from extremely different political views. The core question here, and I haven't seen it exposed, is when and under which circumstances can a certain region of a current state be allowed to become independent. Spain defends that once a majority of Spanish people decides they can, while most catalans (according to polls) want to have that sovereignty. Up until now sovereignty has been decided by force; if you are strong enough you have it. Catalonia is pushing for changes on that respect, trying to execute that sovereignty even though Catalonia does not have currently the strength to defend it. Whether the reasons for independence are or not legitimated, the real question is when and how a certain territory can execute self determination without the need of a war. As far as I know there are no cases where the independence has been accepted from the country where the territory wanted to split from. Spain has multiple examples where they didn't accept independence (their former colonies, for instance, or Kosovo more recently).