I think, if you were ok with a white woman (Scarlett Johansson) playing an Asian character (the Major) you are a racist. Also, if you had a problem with a black man (Idris Elba) playing a white character (the gunslinger) you are a racist. Wait... Something about that doesn't sound right.
But The Major is supposed to be Asian. Like its even a thing in the movie that we see shes supposed to be Asian.
The Gunslinger is just a guy. His race has nothing to do with his character or where hes from, so he could be played by anyone.
Yall always get upset when a black character takes what would be thought of as a traditionally white character, but then you all ignore the shoehorned in white protagonists (looking at you Gods of Egypt) or the white actors who take roles that are LITERALLY Asian people.
Just for the record there is actually a pretty important relationship with another major character in The Dark Tower that does involve race, mainly him being a white male.