The main reason so many "Star Trek" fans took issue with Benedict Cumberbatch's casting was that he'd be whitewashing one of the few popular characters of color in science fiction. On the original series, Khan (Mexican actor Ricardo Montalbán) is of Indian descent, with Lt. Marla McGivers (Madlyn Rhue) speculating that he might be Sikh. Though the production had attempted to hide the true identity of his "Star Trek" villain, audiences knew that Cumberbatch would be playing Khan Noonien Singh, and "Star Trek Into Darkness" ultimately fumbled its Khan mystery.
To this day, fans on Reddit are still perplexed as to why "Star Trek Into Darkness" seemingly never seriously considered any Indian actors for the role. Some have charitably argued that this was an instance of color-conscious casting, with J.J. Abrams not wanting to depict someone from South Asia as a terrorist. However, u/Azselendor alleged that Cumberbatch's hiring came as a consequence of a studio mandate that the villain be name talent (at the time, Cumberbatch had made waves in both the U.S. and the U.K. for his work on "Sherlock").
While Benicio del Toro would have satisfied this requirement, it appears he wasn't willing to agree to the pay Cumberbatch did. Though there's no official record of how much either actor was offered for the role, it isn't hard to imagine that del Toro — a two-time Oscar nominee — was more expensive than a rising star from across the pond. That said, even if Cumberbatch was a more cost-effective solution to the production's problem, that likely won't excuse the whitewashing for most fans.
