Originally Posted by kevin
Marcus acknowledges he took a 'tactical risk' in awakening Khan because he wanted his specific abilities to respond to, as Khan put it 'an uncivilised threat in a civilised time' but I can't actually recall what 'Space Seed' said about his rule.
In one sense a tyrant is a tyrant and he was excised for a reason. I would have to go back to the episode again. Khan in TWOK (or in fact STID) may not be the most reliable source of information about himself given he already managed to blame Kirk for his own fate. And he was quite blatantly murderously intentioned in 'Space Seed' itself.
That said, the term Eugenics Wars seems to indicate some issues.
In Space Seed, once they know who he is they have a little conference and it's then that they mention that he was the "best of the tyrants". They are drawing from history as opposed to anything Khan tells them.
That's not to say that the original Khan wasn't brutal, he most certainly was brutal and ruthless. He just wasn't into genocide for the sake of genocide. He wanted to subjugate and rule.