The first episode of Star Trek Continues. Original series actor Michael Forest reprises his role as Apollo
I think it would have been more in the spirit of Star Trek that Khan stayed in alliance with Kirk and that maybe it was Marcus who compelled Khan to do the killings. And that in the end Khan volunteered his blood to save Kirk.
Then they could just let Khan and his crew go in the crippled Vengeance because like Kirk and co maybe Khan learnt a lesson.
Well of course they would write it a lot better and less lame than I described.
And I'd even probably like Marcus to be less villainous and more pressured by having to defend the Federation from Klingons, Romulans, time-travellers etc. And reluctantly sacrificing Kirk and his crew rather than seeming to take some satisfaction from it.
Well, perhaps the writers could've taken the risk; it's nice to be surprised like that. In any event, Khan may not be able to help it that's he's an over ambitious super-man who is compelled to use his superiority to rule and/or destroy. The "nature/nurture" debate gets a bit muddy when Khan is a genetically modified or created wholly test tube creation that was given his abilities and traits by possibly good intentioned, but flawed 20th century humans. The drama of these concepts can be compelling, but probably more so suited to a Trek TV show rather than the big-budget action movie version of it (not said in a derogatory way, just the nature of a film to has mass market appeal)
But I, (and my party I attended with) were at least able to feel empathy for his plight about having his crew used against him. My suspicions were that Khan had contempt for all the 23rd century people he came across, just some more than others!