Harry used to admire Dumbledore. Spent a long time enchanted by how wise and kind he was, just like the rest of wizarding Britain. After the war, though, after Dumbledore died and Voldemort died and things calmed down and peace settled in... It all started coming out. Harry was one of the people who helped unravel the old bastard’s web of lies and manipulations. Harry, like everyone else, was repulsed by it all. Made sick by the mere idea that he used to worship this man.