Mental illness and abuse

Not always. I'm sure my mom didn't realise how badly she was fucking us up. And I don't always know, either. I try not to hurt others. I try.

Yes. Many can be sociopaths, as well as sick.
See the term "coercive control", and compare it to "sociopathic".
A bipolar or borderline person can easily make a lifestyle of abusing others -. That's a topic for study.