I'm curious how far this "spot on casting" should go. Kirk is a Scots-American. Shatner is Jewish-Canadian. Should they have passed him over in favor of Scots-American? Or perhaps Kirk is Jewish and Pine is wrong for the part. Spock's human ancestry appears to be British. (Mother is a Grayson, ancestors are Doyles or Holmes) Are the Jewish-Russian Nimoy and Italian-Irish Quinto therefore wrong for the part? Then we have an New Zealander of German ancestry play the Scots-American McCoy!!!!
You hit the nail on the head. People will insist that this doesn't matter because they're all "white," which simply underscores the problem with how people - and certainly trekkies in particular - see "race."
If one can't accept Cumberbatch as the fictitious Khan in a story, one has a problem - the filmmakers don't.