Emotional cut offs/discards, declarations of "Leave me alone!" Etc, splitting black... .are they just prolonged STs in disguise? Regardless, it's all abusive.
No, I don't believe it is. I think it is more about someone trying to regulate and/or avoid volatile emotions that are ripping them apart any way they possibly can. For a pwBPD that can typically include "deleting" someone from their life like they never existed, painting them black, smear campaigns, or any other number of maladaptive coping mechanisms. Yes it can be abusive, incredibly hurtful and at times cruel.
Understanding why someone might do this helps to cope with the pain this type of behavior. To that end, how can we help you understand what drives this type of behavior?