I think it would be helpful for people to understand that whilst the views of the OP are apparent in some settings / professionals they are not universally shared by mental health professionals. I've worked with people with personality disorder diagnoses for coming up 30 years in a range of settings so am offering my perspective as an alternative. I'm doing this, not to undermine the OP but to (hopefully) offer more optimism.
There is a lot of controversy around the diagnosis of personality disorder, particularly around the tendency for complex PTSD and ASD being misdiagnosed as borderline personality disorder regardless of how far into the 'system' they get. I've seen it a lot.
There has been a real drive for improving understanding of people with a diagnosis of PD across a range of services to try and keep people out of hospital as long as possible and some great work has been done around this.
My view is that people with a personality disorder have psychological needs which are usually currently treated in a medical and behavioural way because that's how most people are trained and services are set up. They don't 'fit' with or respond to that model so behaviour is labelled rather than understood and behaviour can escalate and relationships break down.
By the time people find themselves in forensic services their patterns of behaviour and schema are even more entrenched so therefore it can take many years for improvement to happen, but it does. People can and do go on to lead fulfilling and normal lives if they have the right support at the right time - and this might look different for everyone.
I just wanted anyone with a PD diagnosis or with relatives with a PD diagnosis to understand that recovery is possible and it's not all negative.