Considering proportionality, pinching a sibling shouldn’t result in corporal punishment at all. Anything for me is not proportional, as an adult hitting a child, it is nothing but pure bullying. I was spanked once and my father deeply regretful. He should have been. I'm a pacifist now, thanks to my mother who became a Quaker in part, but hitting child represents the loss of control of the parent and is not understood by the child. It is now proven in multiple studies that it teaches nothing but violence. However, I'm glad your father lived in deep regret and showed remorse. That is critical to forgiveness and redemption and shows he understood he went to far.

Thanks, your story is deeply moving and very well told. Thanks to your insights and skills, many will reflect on this topic.