I think it's important to note the difference between outrage over castings simply from a racist view because the actor is a certain race (E.G. Finn and Rey in The Force Awakens being newly introduced characters, there is no reason they couldn't be black or female)
Or because previous established material make it a strange or unsuitable choice to give that particular casting role to that particular actor (E.G. Michael Jordan as the Human Torch, not just because the Human Torch is a previously established white character, but because the Human Torch is supposed to be the biological brother of the (white) Invisible woman, which really messes up the continuity unnecessarily.)
One is definitely racist and sexist, the other can be just a legitimate concern for the character's continuity and place in the previously established universe, which I don't see as wrong.
It should also be noted that people on the internet love to complain about any casting choice for any character for whatever reason. Heath Ledger was chastised for taking the Joker role.
Jared Leto was chastised for taking the Joker role.
Ben Affleck was chastised for taking the Batman role.
Jesse Eisenberg was chastised for taking the Lex Luthor role.
Andrew Garfield was chastised for taking the Spiderman role, as has been the steadily younger Aunt May actors, and the new teen Spiderman, whoever he even is.
All these actors were white, all were chastised because they didn't perceptibly fill the shoes or fit the concept of the pre-established character they were playing. Most proved the doubters wrong, some have still to be proven, but all hit on controversy over their physical appearances, if the actor happens to also be a different race from their pre-established character such as Idris Elba as Heimdall (Who was awesome in the role) it will raise eyebrows and lead to questions over the actors suitability in the role simply because it's a deviation from the source material, and too many deviations lead to terrible adaptions.
Richard Gozin-Yu said:
[snip]
Counterpoint: Slumdog Millionaire. Try something new, it might work.
Slumdog Millionaire cannot be used as a direct counterpoint to Exodus: Gods and Kings in regards to Ridley Scott saying he would not get Hollywood execs funding his movie if it was all unknown Middle Eastern actors, because Slumdog millionaire cost $15 Million and was bankrolled in the United Kingdom (The lead actor is actually a British national - Not a native of India!). Exodus cost $140 million and was bankrolled by Hollywood in America.
It can and should, however, be used as an example to prove that non-white films can do excellently in America and beyond; Slumdog Millionaire made $141 million in U.S. Box Office sales, whereas Exodus made $65 million (US sales only). There is a clear sign that a movie set in the Middle East, without white actors can be much more successful than an all American cast movie, but then it's not the Escapist commentators we have to convince about this, it's the Hollywood Execs.