Khan tortured Carol Marcus's science team to obtain information; and then he killed them because he just felt like it.
But wait - he was always ready with a little narcissistic speech or a Shakespeare quote when putting a brain eating bug in your head, etc - which makes all the difference in the world, of course. He was just misunderstood - no savagery to see here, folks; move on.
That was Khan from "The Wrath of Khan" after he spent 15 years on a barren world where he was forced to watch 20 of his loyal followers and his own wife die a painful death. I'm not dismissing what he did in TWOK, only that if it wasn't for Ceti Alpha Six exploding, things would have been very different.
Your examples only managed to show Khan could restrain himself when it was to his advantage - as would be expected from the conqueror of half of Earth. How many millions died for Khan's delusions of grandeur in those wars, Jeyl?
First off, it was a quarter of Earth. Not half. And if millions died during the take over, why doesn't anyone in Space Seed mention it?
SPOCK: In 1993, a group of these young supermen did seize power simultaneously in over forty nations.
Simultaneously in over 40 nations. This sounds more like a quick and precise coup to take over these nations without resorting to an all out war. If there was any killing, it would be more along the lines of facing resistance from the nation's forces, not random acts of bloodshed. And if you don't think Khan didn't do things in a non-bloodshed kind of way, look at how he took over the Enterprise. No armed conflict, no bloodshed and no killing. Just knock them all out. And if Khan and his supermen were in fact responsible for millions of deaths, why do the crew have admiration for him? Keep in mind, they're referring to history written by those who defeated Khan.
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.
You think anyone there would be an open admirer of Hitler, a man who really did commit acts of genocide on whole cultures of people?
BTW - You actually attribute humanistic reasons to Khan being forced to flee in order to escape the consequences of his rule at the hands of his ex-subjects/the people he failed to enslave? Really?
Uh, slaves? I don't think slavery was ever part Khan's style.