Why does Charlie's dad abruptly stop the car on the way to Ohio? What personal connection does Charlie’s dad have to this topic that causes him to react this way?

Charlie’s brother and sister have an argument in the car about domestic abuse. Charlie's brother tells his sister, "Kelly believes in women's rights so much that she would never let a guy hit her. I guess I can't say that about you." Dad stops the car almost instantaneously and ends up sitting between them to stop the fight. Charlie's dad was physically abused as a child, and that experience made him strongly averse to physical punishment.