Sure, I get that self-determination is a human right and I support that. But wouldn't you agree that there should be a balance between the right to self-determination and the territorial integrity of sovereign nations (in our case, Spain)? If there's too much focus on the latter, a state becomes oppressive; if there's too much of the former, then there is theoretically nothing stopping a country like Spain from looking something like this sometime in the future. Sure, you could argue that that won't happen and I can't declare my neighborhood independent because it doesn't have a unique language, culture, etc., but that slippery slope is there and I think ignoring it is a grave mistake. The concept of "nation" is much more arbitrary and fluid than nationalists (including Catalan ones) believe.

In my opinion, there are cases where secession from a sovereign state is morally justifiable (e.g. from an undemocratic dictatorship) and cases where it is not; in my opinion, Catalonia belongs in the latter category.