I'm diagnosed with BPD and met (quite some) other people who were diagnosed over the years. I think your theory is bullshit – but not in a rude way, it just doesn't fit what I know about BPD and the women diagnosed with BPD I got to know.

Generally, I would compare mental illness to the personality theory of temperament (in this case flavour of neurodiversity) + experience

Modern treatment methods often follow a bio-psychological or bio-psycho-social model. This is a oversimplification, but BPD is usually a biological/genetic predisposition to be more emotional + bad experiences in your childhood, leading to strong negative emotions and the lack of mechanisms to regulate those emotions, which cumulates in impulsivity, unhealthy coping mechanisms etc later on.

There's overlap with the vague concept of hypersensitivity and ADHD; there's differential diagnosis too, which is "hey, this can be similar to that, let's diagnose properly before we do anything"; and there's comorbidity.

I agree that trauma plays a big role, and I would go so far as to claim every BPD person is traumatized in a way that justifies therapy, but PTSD is a specific diagnosis, just like autism is.

I think this as well, though I have no formal training in psychology. My perspective comes from a lifelong interest in learning across fields and from having several family members who struggled with mental health, often dismissed as hysterical, crazy, over-emotional, or immature. Decades later, many of them received diagnoses of comorbid autism and CPTSD. I believe that within the next 5–10 years, assuming the DSM can be inured against political editorialization, autism diagnoses will be further refined and the spectrum will become more granular and specific.

Ah the multiple personality serial killer trope. Classic, fallacious, and not the least bit problematic.

Only one of them is out to kill you though. The other is a cook and is cutting onions while another just had the most masive shit of her life.

Yeah, but what about three legs?