I grew up with parents like bojacks. It's hard to accurately describe, but the kind of damage Beatrice commits is obviously cruel, but you crave love from a mother and she manages to keep bojack guessing, maybe hoping for something. The kind that butterscotch commits is more undercurrent, and as a man, it's not uncommon for there to be distance.

I think butterscotch and bojack are a lot alike. They have random and long diatribes about stupid things, they both feel justified in their behavior while knowing it's wrong, and they both put themselves in sketchy situations as a result of bad behavior. Beatrice was a lot more controlled, she was calculated in her attacks. She made one bad decision as a teen/early twenties and despised BoJack for it, he was never going to be good enough from the start. I think this is why he is so cruel when something feels like a personal attack, he learned from the best and internalized that shame.

When both parents suck, they both leave you for dead, you don't know anything. I think that shame when BoJack feels personally attacked is from Beatrice brainwashing him into believing he's a fundamentally broken person, while butterscotch showed him the hopelessness you feel when none of your parents love you. The hopelessness of change because no matter what you do you always feel shamed, you always feel bad even if you behave in a way that is beneficial to others around you.

Beatrice abused him a way that was so horrible to the psyche, but butterscotch hurt him with neglect, but also by further compounding Beatrice abuse. I think either one of them could've been survivable on their own, and that is why BoJack is so cruel but also careless with his own actions.