Well, my feeling about calling BPD and 'illness' is that I don't think of it as something I 'have' but rather the way that I am, or tend to be. When painted with too broad a brush, I feel like the (sometimes) very small and always very important issues that drive my perceptions and responses can get overlooked and therefore not addressed.
I 'have' BPD isn't helpful to my learning about my many fears, such as fear of exposure, fear of failure, fear of being thought of as stupid, fear of intimacy which also drive my wanting to control, wanting to avoid (another form of control), etc.
In my therapy we only very briefly mentioned BPD and only because I brought it up, after reading a book and feeling that BPD fit me or I fit it. lol. Anyway, my therapist agreed and had thought that for some time. She suggested not getting too hung up on the diagnosis and we've never mentioned it again. It just isn't important and doesn't define me, even though it does describe me.