Firstly, anyone who thinks Robert Downey Jr is the real IronMan is just plain silly. Ozzy Osbourne already revealed his secret identity loooooong before him when he said (plain and simple) "I am IronMan". :P
But as for Major, that is the same thing as my Alita argument. Both of them are cyborgs. Major is a human brain inside a machine. Alita's head was found on the scrap heap and then she had a body fitted to it... so how in the world can you cast a wrong ethnicity when casting those roles? It's even more silly than thinking Robert Downey JR is IronMan. ;)
This is exactly why I say that people who complain about whitewashing in this manner are just looking for something to complain about, nothing more.
If you want to complain about all the absurdities out there then I can pile on loads more but I was specifically speaking about whitewashing in this instance as this is a sore spot for me on multiple levels (story for another day).
...but if I were to add to your examples of how stupid people can be, though, I would include this one woman who insisted that anyone who watches Harry Potter is going straight to Hell one day because it is a movie about a boy who does magic and magic is the work of the devil. Thus, by extension, Harry Potter is a movie that praises the devil and all who enjoy the movie needs to have someone pray for their souls... Yeah, that one I actually heard in person. :O
Another one I heard in person is that Pokemon is the devil's work also because it causes you to love and adore monsters. Anyone who likes the Pokemon Go game or the card came or TV show or anything in the franchise are all doomed to an eternity in Hell for loving false idols created by the devil. Riiiiiight....
So yeah, there are some people out there with some pretty far fetched beliefs and there are likely going to be a lot of people who don't agree with what I am saying, accusing my views of being as narrow minded as those views I just listed. I don't know about you, though, but I tend to hear about whitewashing a lot more than damnation by Pokemon and thus I decided to share my feelings on that subject specifically since I have some strong opinions on it.