Blair supposedly changed his views of the British Empire and started hating imperialism after spending time in Burma and seeing the oppression of the locals. That transpired years before he started writing under the pseudonym George Orwell.
Leftists sometimes consider nationalism 'good' when it is nationalism of a small nation against an imperium (or minority ethnicity against a nation state), but 'bad' when it is a powerful nation trying to conquer its neighbors (or opressing its ethnic minorities). But in facts, both of these nationalisms are based on the same toxic concept of ingroupness based on shared ethnicity, language and culture, in contrast of ingroupness based on shared commitment to universalist ideas like freedom, rule of law and democracy.
OTOH, it is likely that the real reason why countries really work is because of some level of nationalism, as commitment to universalist ideas is primarily a thing for elites, while ethnicity-based tribalism is much more primal concept.
Is the latter not also nationalism, if you believe that those ideals create a group that is worthy of self-determination? Maybe it deserves its own qualifier, such as ideo-nationalism, to distinguish it from ethno-nationalism, but does the motivation fundamentally change what it is?
> OTOH, it is likely that the real reason why countries really work is because of some level of nationalism
I think you're probably right here. The question I have is if you can make that nationalism about something other than ethnic groups?
Imo, the catch is that by prioritizing ethnic cultures, you then allow them to supersede the national identity. Ethnocentricism is the default thanks to our monkey brains and in the absence of reinforcement, or the presence of discouragement, it'll probably win over other identities.
I wonder if the melting pot doesn't deserve a reboot. Everything else seems to be getting one these days.
Who decides what a nation is can be a bit tricky from time to time. Who do NOT decide is much easier to answer. In both of your examples, it is clear without a doubt that the people who inhabit the said geographical regions are the ones to decide. Not the Frenchmen from Paris or the Castiians from Madrid.
If the people of Brittany decides that they want Brittany to remain as part of France then it simply means that they do not support Breton nationalism. From a nationalist moral point of view, it is up to the people of Brittany to decide. If a French nationalist wants to keep Brittany as part of France against their will then someone must tell that "nationalist" that he is practicing imperialism rather than nationalism. If a Breton "nationalist" wants to annex all of France to bring it under Breton rule then he is an imperialist rather than a nationalist.