Probably in Khan's favor, even.
Many of you seem to proceed from the assumption that Khan was a so-called bad guy. But the dialogue does not support this at all.
Let's not forget what was said about Khan in the episode itself:
Kirk: "This Khan is not what I expected of a twentieth century man."
Spock: "I note he's making considerable use of our technical library."
Kirk: "Common courtesy, Mister Spock. He'll spend the rest of his days in our time. It's only decent to help him catch up. Would you estimate him to be a product of selective breeding?"
Spock: "There is that possibility, Captain. His age would be correct. In 1993, a group of these young supermen did seize power simultaneously in over forty nations."
Kirk: "Well, they were hardly supermen. They were aggressive, arrogant. They began to battle among themselves."
Spock: "Because the scientists overlooked one fact. Superior ability breeds superior ambition."
Kirk: "Interesting, if true. They created a group of Alexanders, Napoleons."
Spock: "I have collected some names and made some counts. By my estimate, there were some eighty or ninety of these young supermen unaccounted for when they were finally defeated."
Kirk: "That fact isn't in the history texts."
Spock: "Would you reveal to war-weary populations that some eighty Napoleons might still be alive?"
So Khan is compared to Napoleon, a leader of good repute who is widely admired in the 21st century still. He is compared to Alexander, a leader of mythical proportions. Both killed an awful lot of people - but any modern leader has the capacity to do much worse, and most have indeed done so. Trying to nail down Napoleon or Alexander as a "butcher" just puts you in the loonie bin, by modern sentiments.
Kirk: "You fled. Why? Were you afraid?"
Khan: "I've never been afraid."
Kirk: "But you left at the very time mankind needed courage."
Khan: "We offered the world order!"
Like Kirk points out, Khan uses the language of tyrants. But so did Winston Churchill and a long string of US presidents in times of national crisis. Kirk is playing games here; he's not really interested in passing judgement, but merely in tripping Khan into exposing himself.
Kirk: "Name, Khan, as we know him today. [..] Name, Khan Noonien Singh."
Spock: "From 1992 through 1996, absolute ruler of more than a quarter of your world. From Asia through the Middle East."
McCoy: "The last of the tyrants to be overthrown."
Scott: "I must confess, gentlemen. I've always held a sneaking admiration for this one."
Kirk: "He was the best of the tyrants and the most dangerous. They were supermen, in a sense. Stronger, braver, certainly more ambitious, more daring."
Spock: "Gentlemen, this romanticism about a ruthless dictator is-"
Kirk: "Mister Spock, we humans have a streak of barbarism in us. Appalling, but there, nevertheless."
Scott: "There were no massacres under his rule."
Spock: "And as little freedom."
McCoy: "No wars until he was attacked."
Kirk: "Mister Spock, you misunderstand us. We can be against him and admire him all at the same time."
Our heroes are really pulling Spock's leg here with their "defense" of Khan's virtues, obviously. Scotty gets it started with a mischievous look on his face. But what they say is apparently factually true. Remember that Kirk loathes the 20th century in general (see his previous comment about 20th century men), even if he romanticizes the 19th century United States to a degree. Khan rises above Kirk's standards for that century, and while that's not much in absolute terms, it still paints Khan as a saint of his times.
Khan's attitude towards "freedom" is unclear. Are we talking about McCarthyism here? Or Berianism? Good old-fashioned monarchism with freedom of thought but no freedom of press?
Later Trek shows that Earth wasn't exactly heading for the better after Khan left. "The" tyrants were overthrown, but democracy didn't win, and things got worse before WWIII put an end to everything and Vulcans then apparently sorted it out.
Is Khan a Rommel to Kirk - a good guy fated to exist as part of an evil movement (in terms of myth, with the facts of the matter irrelevant)? Or is he something better or worse? Well, he's Napoleon and Alexander... If he were Hitler, surely Kirk would bring up the matter.