The point I was making is if someone hires a Mexican to play a Sikh, then casting an Englishman is no different. Some people have a weird double-standard about Khan's casting.
I don't think it's weird. In general, casting a white person as a character who's supposed to be Asian is a troubling practice, because it's been going on for a long time and has been a form of institutionalized job discrimination against Asian actors. It was just as wrong in the '60s as it is today. The point is that by now, we should've learned better and stopped doing it. It can be rationalized away in-story in the case of STID, but that doesn't mean it wasn't a problematical choice in real life.
The actual weird double standard is going on here in the present. Lots of movies these days are casting nonwhite actors as characters originally created as white in past decades -- Kingpin, Lana Lang, Pete Ross, Nick Fury, Heimdall, Perry White, Felix Leiter, etc. In those cases, old racial biases are being corrected and casting is getting more inclusive. And yet recently there's been a spate of movies where nominally nonwhite characters have been played by white actors -- the Mandarin (though that was an in-story satire of yellowface casting), Khan, Tonto, the Shredder in Michael Bay's upcoming Ninja Turtles movie. (Although a couple of those were offensive racial stereotypes to begin with.) And that's in the wake of the casting controversy over The Last Airbender a few years ago. So there's this strange and disturbing backslide going on in many films at the same time that progress is being made in others.