There are lots of people out there who are assholes to their own family members and they aren't obligated to tolerate them just because they share their genes. People are generally expected to try harder/put up with their family members, but if there's clear mistreatment, why should they?
It's societal norms that say rising against injustice within a family reflects badly upon said person. Regardless of situation.
Just because someone has the choice of cutting out a family member doesn't make that a privilege and your situation worse. Everyone's family is different.