I'm British, and I'm proud of the UK.
It's not perfect and has done some bad things in the past but, on balance, it's a good country (lots of illegal immigrants no doubt agree with me because they're coming here in rubber dinghies, lol).
We ended the Transatlantic Slave Trade, much to the dismay of African chieftains and kings.
We helped wipe out Nazism, we did the world a big favour. We gave conquered territories their independence - this is atypical behaviour for empires.
TBH, it's fairly usual for people to be proud of where they grew up - Homo sapiens is a territorial species, I think it's in our DNA to feel that way.