In Harry Potter and the Order of the Phoenix, why does Dumbledore say Harry is not as angry as he should be?
The reason for this is that Dumbledore did not tell Harry about the prophecy that Trelawney made before Harry was born. Dumbledore wanted to protect Harry from knowing about the prophecy. By doing so, however, he left Harry in ignorance of things that he maybe should have known. Because Harry did not know about the prophecy, he got fooled by Voldemort into going to the Department of Mysteries. Because he was fooled, Sirius died.
So, Dumbledore thinks Harry should be more angry at him than he is. Harry should be mad because Dumbledore helped cause Sirius's death by not telling Harry about the prophecy.