Ron, Harry and Hermione are always doing dangerous, mischievous things that they shouldn't be doing. While doing these things, they make it seem fair, and right, and safe for them to be doing it. From their perspective, it is. They make it seem safe and right to the reader of the book. They feel that there is nothing wrong with what Harry, Ron and Hermione are doing.
In the 4th book, during the Yule Ball, Ron and Harry overhear a conversation between Igor Karkaroff and Severus Snape. They find out that "something" (that turns out to be the Dark Mark) "has been growing clearer and clearer for months." Snape tells Karkaroff to flee, but that he will remain at Hogwarts.
Of course, Harry and Ron can't help but get involved. What were they talking about? Since when were they on first name terms? And this only adds to the suspicion that Karkaroff is a Death Eater, and their hatred for Snape.
As the reader, and as Harry Potter is the main character, you must agree with him and Ron. You automatically assume that they are correct. It's totally their duty to get involved, and find out every bit of information that they can.
But what's missing? It's the thought that they maybe shouldn't get involved. It's the thought that what they are doing is dangerous, and that they should inform the headmaster immediately. It's the though that Hermione Granger sometimes expressed in the first book, before she grew close to Harry and Ron. It's the perspective of someone outside of Harry and his close friends.
It's a good thing that this perspective is missing. If it were here, it would completely ruin the story.
If that voice was there instead of the perspective of Harry and his friends, the reader would be disappointed. They would doubt the strength and passion of Harry and his friends. Do they really want to go through with finding that out? What about the risk? That is not how you are supposed to feel at all. You are supposed to be excited,and supporting, and eager for adventure. You are supposed to feel strong emotion. If the other voice was their instead of the voice of Harry and his friends, then it would be 2 sides contradicting each-other. They would cancel each-other out. The actions of Harry and his friends would weaken, due to the words of perspective.
If that voice was their in addition to Harry and his friends perspective, than there is a chance it wouldn't overpower the original voice. The original voice is Harry, Ron, Hermione, sometimes Ginny Neville Sirius, and Fred and George's view. That this danger and mischief is okay. This voice is often shared by the reader. Because of this, it would be hard for an opposing view to overpower it. But, it would still weaken the view. If there was a voice when Harry and Ron listened to the conversation of Snape and Karkaroff saying...
"But they shouldn't share the information, or go into it deeply, because it's private and could be very dangerous"...
than the entire effect would not be as passionate and exciting.
