@barnebyj,
Hitler caused great harm, but without him we wouldn't have jetpower, advanced areodynamic understanding, advanced radar navigation, sonar, atomic power, free ways, computer ..etc ..etc.
Not that it was his inventions, but caused the alliance to invent things at any cost to wage war against him.
Sometimes we have to be cynical and sacrifice to do good, and those who think they do good, do evil in their ignorence and naivity. Just look at parents who spoil their children rotten in the naive belive that they do good, often children end up fat getting diabetes, getting bullied in school, and can't take care of themselves in life because they were never taught how.
Many chatholic children home never taught the kids how the real world was like, and being locked up in a children home doesn't teach you anything, thus these kids were ignorent when released to the real world, and was subject to scams and misery.
Good and bad are very subjective and relative terms, usually spoken out of ignorence.