Why so much cheering for a ethnic-nationalist party?
How is Cs an "ethnic nationalist" party? They've adopted harsher rethoric against peripheral nationalisms but that's it. I don't think they are worse than say, the 00s PP, which collected signatures against the Catalan estatut.
Or the old UPyD, which actually did have in it's manifesto to take away some devolved powers (most notably healthcare and education) and give them back to the central government.
If it were VOX we were talking about (or God forbid, some of the tiny fascist parties like say, Falange, aka Franco's party) then sure. But Cs is just another liberal party with harsh rethoric against peripheral nationalism like UPyD.
Cs has embraced the flag to win votes and that's good, but inevitably they will turn right, you can not pretend to stay with conservative pp voters without being tougher than them.