The fact that it happens so often and more importantly is widely accepted, suggests that a discourse however historically accurate is absolutely pointless. So instead of a debate let's just create our own casting for films to illustrate the point of how it feels to be mis-represented.
Let us create a Henry VIII film, still set in England. We will have Henry and all the English roles played by Chinese people. Anyone European is to be played by Samoans...and oh yes this film is to be labelled as being the most historically accurate picture ever made.
Chariots of Fire, once again set in England, re-made where the entire cast are played by Bangladeshi people. Any non-English roles are to be played by people from Singapore.
Saving Private Ryan, the entire American army are to be played by Iranians.
12 Years A Slave, all the slaves are to be played by Europeans and the White American parts are to be played by Africans.
Exodus: Gods and Kings; A biblical story set so far back in the history of the world, that the 'culture' playing the parts now, didn't even exist. That very same culture are to play all the important parts of course and then the cultures that were actually born of the entire CONTINENT that the film is set in and did exist, you know the ones that occupied and lived in that location before the advent and invasions of cultures such as the Persians, Greeks, Romans or the existence of the Ottomans, yadda yadda yaaa are to play the slave and 'lower' status roles.
There won't even be the casting cop out of having a cast look like the current people of Egypt, who's look only appears after the Arabs had finally grown in significant numbers to be a mighty force and come into the land to shake-up the genetic make-up. No we're gonna keep it truly unreal and perpetuate more lies. Why on Earth does the Hollywood system back the re-writing of history to such stupid degrees? As a kid for years I believed that the Native American's were such a villainous people and that Russians were the natural enemy of the world.
When Casting Doesn't Matter
Even though it can be annoying when a character from a book is described as one thing and portrayed on screen as another, I don't mind altered casting when it bares no change to the overall premise. If a story has no emphasis on gender, race, age, nationality or sexuality - then knock yourself out with your casting choices. Rising Sun, The Hunger Games, Daredevil and the new Fantastic Four film currently in production have all switched things up, but not to the detriment of the story.
Alternatively I don't need to see a black James Bond or a female Dr. Who. What for? The characters were conceived with specific details that create who and what they are, if you change significant factors then you have a new character. A black James Bond for me is like having a white Shaft, his backstory and life path change dramatically. Look at the backstory 007 had in Skyfall, what are the odds of a Chinese Bond having that ancestral past in Scotland?
Inclusion is great, correct representation even better, but the real appreciation would come in the form of for example creating a 00 agent with his/her own identity and history. Or bringing about a female Gallifreyan timelord with her own mythology. The people who are not being represented are not overly-sensitive, they don't need to be the key people in every production or even be in every production, but if you are telling their story you, then you have to respect the fact and place of their existence or don't tell the story at all.