Culturaly: Spain and all governments have tried to kill our language, Until 40 years ago, we had just forbidden from using our language, celebrate our traditions, etc ... Not to mention the historical revisionism.
One thing is solidarity and other plunder. Also, having to endure that every day we called from "Nazi" to "beggars", Would you stay with someone like that?
Where do you think the English term to welsh comes from? The Victorians tried to wipe out the Welsh language.
On a related subject, for someone apparently so sensitive to political distinctions between culture and nationality, what is it with just dismissing British complexity? "England" has not negotiated with anyone in 300 years. The UK parliament in Westminster has been negotiating with the newish devolved Scots parliament in Holyrood, but that is not England negotiating with Scotland.
It would be more correct to say that all Catalans are Spanish than to claim that England and Scotland are autonomous parts of the UK.