Abuse is never good, especially for the victims and for those who look on with dusgust.
But abuse can help some people realize how bad things are and that they need to make a choice to stay or to leave. It always boils down to the choices we make. I could have chosen to maintain a relationship with my JW mother or husband or religion. I believed, as most victims do, that there was no choice.
One day I was talking to a friend and he said: "Not making a choice IS a choice". Wow! I had to sit with that for almost a week before I realized I didn't like the choice of not choosing. Sitting on the fence is a hard place to be. I waited until it was a life or death choice for me. And I didn't want to be dead so I left.
I think abuse forces the hand that would otherwise remain still, content with the status quo.