Was Dumbledore Actually a Good Headmaster?
The case against
The school under Dumbledore's leadership is objectively dangerous. A three-headed dog guarding a trapdoor is placed in a corridor accessible to students. A basilisk roams the pipes for a year. Dementors are stationed around the grounds. A tournament designed for adults is entered by a fourteen-year-old.
Dumbledore's hiring decisions are also questionable. He employs a man possessed by Voldemort, a fraud, a werewolf who forgets to take his potion on the one night it matters most, and a Death Eater disguised by Polyjuice Potion. Only one of his Defence Against the Dark Arts hires, Lupin, is an unambiguous success.
And then there's Harry. Dumbledore places a baby with abusive relatives, monitors him from a distance for eleven years, and then uses him as a weapon against Voldemort for the next six. The seventh book reveals that Dumbledore always knew Harry might have to die, and he raised him for that purpose.
The case for
Dumbledore was fighting a secret war against the most dangerous wizard in history, and he was doing it largely alone. Every decision that looks reckless in peacetime looks different when you know what he was preparing for.
The Dursleys were the only option that kept Harry alive, because of the blood protection his mother's sacrifice created. The dangerous events at Hogwarts were, in most cases, Voldemort's doing, not Dumbledore's negligence. And the plan to use Harry was not callous; it was the only strategy that could work, and Dumbledore agonised over it.
The seventh book makes clear that Dumbledore loved Harry, and that the burden of what he had to do nearly broke him. His greatest flaw wasn't cruelty; it was the belief that he alone could see the full picture and that keeping others in the dark was for their own good.