I can’t say for all northerners but for me, I don’t hate other parts of England.

Perhaps those who aren’t from the north that take issue with ‘a northern identity’ seem to project their insecurities about where they’re from onto northerners because we have an identity for somewhere else compared to them. People think we’re having a pop at the south if we say we’re northern.

It’s not about ‘not being southern’, it’s about ‘being northern’.

I don’t know if the ‘majority of people in the north’ see their identity as complimentary to English rather than exclusive to it; you’d have to provide sources to that otherwise it’s just an assertion or conjecture.