Disclaimer: I don't own Harry Potter.
Nisi nil bonum mortui. Speak nothing of good but the dead, they say, and we don't. We say his parents were very much in love, but never mention that it wasn't with each other. We say his father was popular, but never mention that he was only popular in Gryffindor, and Ravenclaw and Hufflepuff were outright terrified of him and Slytherin hated him passionately. We say his mother was brilliant, but never mention she was brilliant at the Dark Arts. We say Azkaban left his godfather in a bad way, but never mention that the bad way is really alcoholism. For that matter, we say he was his godfather, when it is really far too likely that he was his actual father. We never mention any of it, because it was long ago and it doesn't matter anymore. All there is left is an undying schoolboy grudge, a convict who might be his father, and a lovelorn werewolf, pining for the man named as his father. Nothing worth worrying about. At least, nothing Harry needs brought to his attention. Let him keep an idealized image of a perfect couple. Saying otherwise would be speaking ill of the dead, after all.