That would imply that Khan was intelligent, or capable of basic self control. He was neither. He was, as I have written before, a rabid pit bull terrier on two legs; who people still love because he combined the idea of being Space Hitler with the fact that Ricardo Montalban was the male answer to Marilyn Monroe.

Khan should not have been given his own ship. He and his followers should have been unceremoniously shoved out an airlock. I understand that Kirk didn't want to do that because Augments were still sentient living things, despite being uncontrollable monsters, and enlightened Federation ethics means we don't do things like that; but in this particular case, refraining from killing him was itself irresponsible, as TWOK proved.