Gonna quickly throw in an epic quote I found on this article.
KJKJ: Gene Roddenberry, with balls of brass, got up on national tv and said, “hey people, if a geneticist took all the best DNA from planet Earth and put it together to make the best human the world has ever seen - he wouldn’t be a white guy.”
This is why I find the casting of a white actor in this role to be so repugnant. They are not whitewashing an Asian role, they are saying that the best genetic material that the entirety of this world and it’s diversity has to offer….still comes from a white guy.
The problem is the term “best”. Khan is extremely intelligent, physically superior, but also extremely violent and hateful. That, in my opinion, does not constitute the “best human being”. He lacks universal empathy. And also, white skin does not define the total genetic material which he may be an amalgamation of so it would be a mistake to consider that the best ”still comes from a white guy”. The argument can still be made against him regardless of his skin color or ethnicity. If he had the appearance of an South Asian, someone could ask does that mean the best genetic material comes from South Asians? This aspect could be but a small part of the genetic makeup (although the most visible). And further more, we barely saw any of the rest of his crew. There could a great diversity among them as that would be a strength for them as a group.
I can understand, however, an argument made that changing the appearance of a character who has already been well established would be a mistake. Star Trek is very much about maintaining continuity of its story and characters, and Khan is a character who was very well defined by TOS and who would be unaffected by the new time-line created by the events of the previous movie. And this is why I had a small problem with the casting decisions, even though I say he gave a very strong performance.