Most people will go along with this, just as they go along with answering questions about firearms in the home that wind up on a kid's medical record. It won't occur to people that this is even in play. Rather than having a conversation with their kid ahead of time, setting the boundaries for who is allowed to do what when and where, they'll just be caught in the moment, and do what the doctor says.
Thus, they will not have in their arsenal, "Thank you for your concern, but Sonny and I have had a conversation about this, and we've both agreed that anything you and he would discuss is to be discussed in front of me as Sonny's father. I am involved in all his medical decisions, and personal matters are family business."