The problem is that the makeup is an excuse to cast a white actor instead of giving an opportunity to a nonwhite actor, and that perpetuates white privilege. Characters are fictional, but actors are real live human beings who need to eat and pay the rent and often have families to support. Roles for minority actors were scarce enough as it was in the '60s, so when someone wrote a character that was perfect for a minority actor and it ended up going to a white person in stupid-looking face paint, that merely reinforced the institutionalized employment discrimination. To a white person who has nothing personally at stake, maybe there's a difference. To a minority actor being shut out of an employment opportunity because they gave it to a white person, there's no difference at all. Besides, casting Montalban as Khan was one of the milder instances of brownface casting in the '60s. Look at The Man from UNCLE's "The Yellow Scarf Affair," for instance, with Murray Matheson cast as a Hindu in an episode that portrays Indian culture in a grossly racist fashion, basically equating all traditional Hindu culture with Thuggee murder cults. They cast an actual Indian actress as his daughter, but she was the only Indian character in the episode who wasn't played by a white actor, and Matheson's makeup looked ridiculous next to the real thing.