I think that's just social conditioning. Some people react strongly to any questioning of their sexuality too. Call the wrong guy "gay" and you have a fight on your hands (although this is often a clear sign that there's some truth to the claim).

People hold very strongly to national identity or racial identity, but again, it doesn't "feel" like anything to be black or Norwegian.

The question of one's "core" is very interesting. I'd argue very strongly that there's no such thing. But that might get a little too metaphysical for the scope of this conversation 😅