Why do people say that borderline personality is the equivalent of sociopathy in females?

Sociopaths are not supposed to have a conscience/ i.e they feel no remorse for their actions. However people with borderline personality disorder often suffer from an extremely low self-esteem. They often feel that they are unworthy and are inherently bad (especially since they see things in black/white). This seems markedly different from sociopathy where it seems unlikely that the sociopath would feel that he is an unworthy person. So my question is why do people say that bpd is the female version of a sociopath?