The responses to the Elba casting are somewhat eye-opening, somewhat unsurprising.
My thoughts on King saying he doesn't care about the race of the character is that it's the "right" thing for him to say at this time. I think he'd prefer the first (possibly only) film incarnation of Roland to be white, like he imagined when writing the series, but his more recent past has been filled with questions about his use of black characters in some of his writings - i.e. either they were throwaway side characters, or they were magical negroes and/or black characters with no wants or motivations of their own who solely exist to help white protagonist(s). I don't blame him for getting behind the casting of Elba. I can't imagine the backlash he'd receive if he boo-hooed the Elba casting. Maybe he truly doesn't care, and kudos to Mr. King if he doesn't.
As for many of the other constant readers who loathe the casting, some of it seems to come from just the fact that he's black, and although there are seemingly logical reasons given, the underlying tone is he's black and I want him to be white like I always imagined him to be. Some of you have said ANY of the other characters can be black, but Roland HAS to be white in order for the story to work, while others have laughably compared the casting of Elba as Roland (a fictional person whose race has nothing to do with character-personality-mannerisms) to a white actor playing Martin Luther King or Malcolm X (two real life black men whose work centered on them being black in America). I know this is not anyone's intentions, but it comes off in a way that reminds me of a saying - all you see is a black man, instead of a man that just happens to be black. That means that although Elba could do an incredible job as Roland, perfectly picking up all of his mannerisms and character traits from the book, the fact that he is not white will overtake any great performance he may bring to the screen.
Of course, the biggest reason brought up for why he should remain white is the character of Detta. Detta has to be able to call them all some "honky mahfahs" to add some conflict to the group and character for Susannah, but how can she do that without Roland being white, right? *sigh*...I absolutely hate the character/personality of Detta Walker. She's just a jive talking, sex-crazed, incredibly racist caricature of a black woman. There is absolutely NO WAY the filmmakers were going to keep that the same no matter who they cast as Roland or what kind of growth as a character she has throughout the book. I saw her character as problematic years ago when reading, and I will not be sad to see that personality gone (or at least dialed down a lot of notches).
--- I say all that to say this, I also would have loved to see Roland being played by a white actor. It's been almost 10 years since I read the books, but reading those books was like a journey where you could almost feel you're a part of the ka-tet yourself, and when you envision the characters as looking a certain way, it can be jarring and, in a way, heartbreaking when the first real visual representation of what you imagined is nowhere to be seen on the screen. However, I am still going to go into the movie with an open mind. The race change is nothing compared to other changes that may happen.