Literally no one said that a minority actor doesn't have the chops to play a traditionally white character.
Denzel Washington, Chiwetel Ejiofor, Will Smith, Mahershala Ali, David Oyelowo, Morgan Freeman, Forest Whitaker, Terrance Howard, Samuel L. Jackson, Don Cheadle, Cuba Gooding Jr., Laurence Fishburne ... All amongst the best actors living today.
Literally zero people have said that minority actors don't have the chops.
I've made a pretty clear argument as to why race changes get an emotional response from fans. It's not about an actor of another race not having the acting ability to perform the character, it's that generations of fans grew up seeing themselves in that character and a big reason is because they identified with them from a physical/visual level. So giving diversity so that another group can have a character that reflects them will always come at the expense of taking it away from an established fanbase.
Now, I'm not saying that I can't see part of myself in a minority character or that a minority fan can't see themselves in a white character ... or that a character's race is their main and defining characteristic. It's not. But it is a big part of a person's identity.
A white woman couldn't play Storm. That doesn't mean that there are no white women who have the chops to play the part. It's just that Ororo Munroe is a black woman. She's a character that little black girls look up to and see themselves in and are inspired by. It would be unfair to take her away from them. Just like it's unfair to change Dick Grayson for no other reason than diversity's sake.
-R