Identity has many different meanings depending on the context, just look at the Wikipedia page:
https://en.wikipedia.org/wiki/IdentityHow it is being used in pg's Identity, I believe, is referring more to a Self-Concept (https://en.wikipedia.org/wiki/Self-concept), or 'How one views one's self.' On the other, statements like "I've often been accused of being overly analytical" and "I already have OCD" refer more to Self-Knowledge, which the Self-Concept Wikipedia article suggests is distinct. The difference is in how we think about how things relate to ourselves, and is critical to what pg is saying.
For example, the article brings up an example in which a thread about programming degenerates into a religious-like war when programmers identify as a "X programmer".
By incorporating X into their identity, or Self-Concept, they are saying 'X is part of who I am.'
By incorporating X into their Self-Knowledge that would sound more like, 'X is something I know.'
The Self-Concept is dangerous because when someone else comes along and says something like "X sucks" the X-Programmer interprets it is "part of who I am sucks" as opposed to "something I know sucks." The latter is easy to dismiss (or discuss), but the former is personal and offensive.
pg warns that the more of these ideas we build into our Self-Concept the more exposed we become. By allowing more ideas into our Self-Concept we create new path ways for others to strike at our primitive, illogical, emotionally biased core. And its not that having that primitive core is bad, it's just that 'sophistication, logic, and rationalization' are slow and take a lot of energy. Presumable, that's why we have that primitive core, because people who try to rationalize threats to their well being are beaten, eaten, and humiliated; they can't react fast enough or keep it up long enough.
So don't try to hit the other extreme, you'll just wear yourself out. But be careful what you allow into your Self-Concept, because your Self-Concept isn't rational.