Some (and I do want to stress the "some") HKers don't want to be considered Chineseby others because China has a bad international reputation. That's it. That's really all there is to it.
It's like the kid with the poor parents who doesn't want to admit to the other kids in school that those are his parents.
Like every ABC (OK, I was actually born in China, but close enough) kid growing up on the East Coast of the US, I went through most of my childhood not wanting to be identified as Chinese. And yes, it happens to all ABC kids. They may not want to admit it, but that's the truth.
But as one matures and defines one's sense of self through introspection, one realizes that one's cultural/ethnic identity isn't up to him/her.
We are born as who we are ethnically. And we all have the right, nay, obligation to be proud of it in the way we have an obligation love and respect our parents regardless of who they are.
Perhaps it is because of this experience that I find it so unforgivable that some HKers deny their Chinese identity.
And before someone says "no, they're just denying their Chinese nationality not their heritage/ethnicity", I'd like to remind them that the law doesn't work that way. So long as someone holds a HK "passport", they are a citizen of the PRC, different from mainland PRC citizens certainly, but a PRC citizen nonetheless. That's not anyone's opinion, that's the actual law.
Yeah, sorry folks, the law is not a matter of personal opinion.