You can also sort of bring yourself to admire the things bad people do. The Nazis, to go back to them, tiring as they are, accomplished some amazing things. They were evil and horrible and nasty you could get, and the harm they did outweighs their achievements by 100000 times, but they still did do some nifty things - or, to say, those under them achieved some nifty things. The German Army fought tremendously well during the Second World War - on a per-unit, per soldier level, no other army of the Second World War fought as well as they did. They lost because their leaders were bone-headed and they took on too many enemies. But the fighting skills displayed by the Germans was pretty astonishing. Of course, it was in service of a truly, horribly evil cause - but still, when you read about what the German Army was capable of, you can sort have a grudging respect for what they managed to pull off. Same with Genghis Khan - he was a horrific mass murderer, but his military skills were something to write home about, because he never lost a fight. Admiring Genghis Khan's skills doesn't mean I like what the guy did (the low number of deaths the Mongol Hordes Killed is about 40 million - and that is the LOW estimate, which isn't that much less than the number Hitler killed in Europe) - but when someone fights well, there's no point in denying it. When someone does something well, there's little point in trying to say "NO THEY DIDN'T" just because they were bad people.
Bad people can be skilled. Evil people can be talented. Look at the Roman Empire - many Historians are fascinated by the Romans, emulate the Romans to some extent, cherish their history and culture. But LOOK AT WHAT THE ROMANS DID. Read the History of the Roman Empire - it was one of slavery and bloody conquest and heavy taxation and sheer misery for those who unfortunately happened to live in the path of the Legions. The Ancient Romans did not have a nice society - not at all. If the Romans were around today, everyone would be calling them horrible, evil people - which is what they were back then. But still - they built some damn nice buildings. Their governmental structure was very efficient for the time. Their armies fought EXTREMELY well. They were the Evil Empire, but you've got to hand it to them that they knew what they were doing - they didn't conquer the known Western World by accident. They were talented, and some of things they achieved take your breath away. But they were bad people.