I personally am against it. I think that a future socialist Spain would be stronger if it was unified, and division would threaten that. I also don’t think the arguments for seperation are that strong and the pro-independence movement is not just left wingers. I think like half of the movement are liberals, like Puigdemont.
But I’m not that well read in this topic so if you think otherwise I’m willing to listen


Spain right now is probably the most anti imperialist country in the EU right now (whatever that may mean) so breaking up Spain would harm that. I’m not sure how left wing the Catalan movement is these days. At least with Basque Country you can expect a mostly left wing independence movement.
Catalonia (and Euskal Herria) are the most important economic regions of Spain as well so a balkanization of Spain would have severe consequences on whatever nation that remains Spain.
Last I heard there was a significant—perhaps predominant—bourgeois faction in the Catalan separatist movement.
So they’re like Albertan separatists?