Yeah, it's one thing to imagine Hitler having a change of heart back when he was a painter, before he really did anything. But let's says he's already done some absolutely unforgivable things, already killed a million people. Then the ghosts from A Christmas Carol show up and somehow convince him to change his ways. There's now a good Hitler, somehow trying to end this vast evil empire that he himself created. The Wermacht is already deep into the Soviet Union. You think Hitler's just going to call up Stalin and be like, "hey, can we just call this whole thing off, call it good here?" And how does good Hitler balance using his power to undo his past actions vs accepting moral responsibility? He could resign immediately, but then he's putting other evil men in charge of the war machine.

Or phrased another way, you get Freaky Fridayed into Hitler's body on July 15, 1941. What would you do in that situation? It's even worse in that case, as you aren't even morally responsible for Hitler's crimes.