What is the context of the particular character is the important question. Is the character's race important to that character? If you have a character that is part of a white supremacist organization, for example, a non-white actor probably won't work. A character that is playing a ronin in feudal Japan should probably not be white. Obviously it's possible to do these things, but it depends on how the character is written.
In many cases, the race of a character does not matter, but in some cases, it is an integral part of the character. Being a fictional character does not mean race cannot be an important consideration.
Idris Elba playing the gunslinger in The Dark Tower? That's fine. The character may have been white in the books, but it wasn't integral to the character. Idris Elba as James Bond? Again, no problem. Bond may have been written as a white guy, but it does not seem to be integral to the character. Idris Elba as a fictional grandmaster of the KKK? That does not work unless the story allows for such a major deviation from the expected or sensible.
TY for your response. It's a good one, and I don't particularly take exception with it because it's the same thought progression I had when thinking about the question I've asked.
That said, the rarefied exception cases you note crossed my mind when I composed the OP, and it is in consideration of them that I included Coleridge's remark. So how do you reconcile his theme with your rarefied cases?
What is the context of the particular character is the important question.
Absolutely, that is the context respondents need to consider and define for themselves and express in their answers.
I'm not sure how the Coleridge quote is especially relevant. I may be misreading his intention; the structure of the language he uses is not something one would normally encounter in modern America. He seems to be saying that he should create imaginary characters, then give them enough realism to allow suspension of disbelief. Wordsworth, on the other hand, took real characters and things and gave them a feeling of the supernatural.
That Coleridge would take an imaginary character and give it realistic traits does not necessarily have anything to do with race. Again, it's all dependent on the context of the particular character. In some cases race might be a way to enhance the realism of the character, in others it might not.
I'm not sure how the Coleridge quote is especially relevant.
Fiction necessarily calls one to willingly suspend disbelief. When consuming fiction, one must necessarily do so because the medium involved is fiction.
Coleridge's axiom notwithstanding, it's a given that the human condition/experience is universal, which is why anyone can relate to joys and pains of others -- individuals and groups -- who are very different from them, be it by race, creed, gender, nationality, nexus, etc.. Thus, for example, if a white dude plays a Medieval Japanese shogun, does his whiteness make able to convey the emotions and motivations necessary to inspire in audience members the affinity with, disdain for, or some other set of emotions attendant to the character's personality and deeds?
Audience members, by consuming a work of fiction, have already agreed to the request that they suspend disbelief, so I say no, and as illustrations of the irrelevance of race I point to the following:
- Argo -- Ben Affleck played Antonio Mendez, a Latino man
- Elizabeth, Michael and Marlon -- Ralph Fiennes portrayed Michael Jackson, a black man.
- Breakfast at Tiffany's -- Mickey Rooney portrayed Mr. Yunioshi, a Japanese man.
- Othello -- Laurence Olivier portrayed Othello, a black man
- Lone Ranger -- Johnny Depp portrayed Tonto, a Native American man.
- Avengers -- Samuel Jackson as Nick Fury, a white guy in comics.
- Thor -- Idris Elba as Heimdall, who legend describes as literally the whitest of Norse deities.
- Cinderella -- Brandy Norwood as Cinderella & Whitney Houston as the Fairy Godmother
- Fantastic Four -- Michael B. Jordan as Johnny Storm who was always a white dude in the comics.
- Prince of Persia -- Jake Gyllenhaal as Dastan, Prince of Persia; I think "Persia" says enough.
- The King and I -- Yul Brynner as the King of Siam; "Siam" says enough.
- Exodus: Gods and Kings -- Christian Bale portrayed Moses, who was of Middle Eastern or African extract of some sort.
- Noah -- Russell Crowe as Noah who had to had to have been of Middle Eastern extraction of some sort.
I've seen the productions above and the race of the character didn't cross my mind as I engaged with the film and the characters' words and deeds in the films.
Yes, fiction requires some suspension of disbelief. However, that does not mean that anything goes. I have all too often gotten into an argument with someone about a work of fiction in which they make the argument that, because some aspect of the work is fantastical, any fantastical aspect must be acceptable. That simply is not the case.
Any work of fiction will have its own internal rules. If those are ignored, it does not matter that the work is fiction, it will still be a problem. So, for example, The Walking Dead is a show about a zombie apocalypse. Zombies are obviously an entirely fictional, fantastical feature. However, were one of the main characters to gain the power of flight, it would be completely inconsistent with the rules of the world that has been created, and would make no sense, despite the suspension of disbelief required for the show.
I have not seen many of the films you list, but I'll make some comments.
Ralph Fiennes as Michael Jackson seems a bit wrong, but Jackson was such an odd character, and his skin lightened so much over the years, and because I have seen that listed as a comedy, it might not be much of an issue in that particular case. I'd need to watch it to really know.
Rooney's role in Breakfast at Tiffany's was horrible casting, is widely considered one of the more egregiously racist characters in Hollywood, and seems like a terrible example. I can see most of your other examples as making sense, but this one seems to actually work directly against your point.
Johnny Depp as Tonto is also a poor example. There was a lot of outrage about the casting. The movie was a flop. Audiences were not willing to attempt to suspend disbelief about the character, because the character's race/ethnicity are integral to who he is.
Samuel L Jackson as Nick Fury took some getting used to. For those unfamiliar with the comics, it was probably not an issue at all. For comic readers who had seen Nick Fury as an older white man for so long, Jackson playing the role was a bit jarring. However, Fury's race is not intrinsic to who the character is, so the change of race was not a terrible thing.
Idris Elba as Heimdall - I didn't know much of anything about Heimdall going into the movie, so his race was meaningless to me. I imagine the same is true of most audiences. I still don't know enough to say if his race is important to his character, although I doubt it.
Michael B Jordan as Johnny Storm was somewhat bad casting. Johnny Storm and Susan Storm are siblings, and the movie had to make them adopted siblings for the move to work. It would have required less change if Reed Richards or Ben Grimm were of a different race. However, this is another example of the issue being one of a long-term pre-existing character story, rather than race being important to who the character is, so in the end, it is doable. Unfortunately, the movie was garbage, regardless of the races of the actors.
It seems pretty common in the US, or maybe even in the West, to think of Middle Eastern religious figures as having been white.

Have an Asian Moses or Noah and that suspension of disbelief would probably suffer casualties here.
It still comes back to context being the key.