I'm not sure I'd call Harry's Black and White vision of the world 'insane'. Consider he was a kid when DuMorne picked him up proceeding to be subtle abusive to him for most of his teenage years. He did not have a solid grounding in any kind of morality, much less a morality of magic right up until he meets the thoroughly inhuman Leanansidhe who persuades him to commit murder. He thinks he killed Elaine, discovers that he has been practicing Evil Magic (TM) and that one more instance of it will kill him. The person imprinting that on him is a centuries old wizard with an iron will, vast skills at magic... who is also terrified that his grandson is going to get killed for being a warlock. Harry thus gets the most puritanical for lack of a better word version of a White Council Education imaginable.
At the start of the series this version of morality stands in start opposition to the authority figure Harry first attached himself to and for whom like most abused kids he must have made excuses and to his Godmother whose later actions got him under the Doom by encouraging him to fight the bastard.
In an odd sort of way the journey of Harry Dresden mirrors that of someone with a strict religious upbringing being let loose in the outside world, complete with finding out the mentor he tried to emulate was not the paragon he thought they were.