There’s nothing wrong with being proud of a specific province/city/community, but any differences in human society can be used for reactionary division. Flags can be used for other purposes than as a symbol of national sovereignty, but a flag is also probably the most identifiable symbol of independence or separatist movements precisely because it can be seen as a symbol of national sovereignty. I think the political significance of flags outweigh any other aspects, if any.

At the end of the day, there’s nothing inherently wrong with having regional flags, but I oppose it.