Criticism is hard to carry.
Imagine if I walked up to you and said, “I can’t believe your mom. Someone should call the authorities on her. Clearly, she doesn’t love you.” My guess is you’d be pretty mad at me. But what if it wasn’t me talking about your mom? It was your dad. Or it was your grandma talking about your dad. Or your mom talking about your stepmom. No matter how old you are, you’d feel it, wouldn't you? I talk to kids who tell me that’s what their parents say about each other. On their behalf, “Knock it off.”