I'm not sure what "core beliefs" means precisely. But if it means beliefs you wouldn't discard even in the face of evidence to the contrary, it would seem good to have as few of those as possible.

I think that he isn't so much arguing against having core beliefs as he is arguing against maintaining a minimum number of social identities. Overall, I think he is taking a rationalist approach.

pg cites being a scientist as a good example of a minimalist objective. He seems to be getting at a social version of occam's razor.

I think identity requires both the internalization of a belief and an emotional commitment to its truth.