Was trying to spot when it went from a general discussion to focusing on Tolkien, and found it as a side-y quip by Hygro that got picked up on, because of course that's what happened. Here goes.
IMO the milk world of Tolkien works pretty well, but it does have a myriad of isses that take it far from the complexity of the real world, race is not the only thing here. It doesn't even represent medieval Western Europe that well, it's more of an idea of what it was as an incarnation of worldbuilding, deliberately glorifying it, which is why I get Hygro's discomfort with it. While I adore a lot of Tolkien's worldbuilding, the general structure of the world is quite simplistic. There's a lot of detail in it, but the world isn't structurally complex in a broad sense. Like, making subdivisions of angels under God adds detail, but it's still Catholicism vs Evil. Tolkien was more interested in emulating mythology, creating languages and inferring that history is one big arrow downwards than creating societes with actual complexity. This doesn't mean they're not good books, it's more that it's not the world to look for if one wants complex society portrayed. It's something to look for if you like mythology, swords and Romantic notions of medieval knighthood, ethnicity and monarchy. There's a charm to having an ascended extra showing up out of nowhere killing Smaug, even if it's kind of ridiculous when you're writing a story, because stuff like that happens a lot in old stories, it's neat to recognize. Later fantasy generally abandoned the simplicity of Beowulf and went more into grays.
For OP, I believe all representation has value, but white representation is so saturated it's not really needed at this point. White people have an abundance of mainstream material to engage with easily. There's so much being produced that they'll never even get to experience all of it, no matter how hard they try. So I don't have much sympathy with angry white men feeling robbed over stuff like this. Let's say they remake the Lord of the Rings and insert more nonwhite characters on the side of Good. There's still one of the largest Hollywood productions in the world, a good production even, where they get to see European cavalry murdering monsters of the Orient heroically.
Still, great world. Just not something you should look for much complexity in, racial or otherwise.
I know Tolkien nerds will punch me over this, and I understand. It's a great setting, and I understand how one gets attached to it. I am attached too. It's just that even slightly more complexity has been shown to be easily possible in most other fantasy settings I've engaged with.
I suspect the same general cause and effect applies here. People are satisfied when characters fit with how they have previously imagined them, but feel anger and disappointment when their expectations are made to fail.
I believe personally it's how aesthetics work in general, and it goes beyond music and even art. There's psychological support for it, but there's some really approachable literature on the matter. I suggest reading John Frow's
Genre, the introductionary chapter outlines how this can be approached on a humanities level (ie understandable for people with a general sense of academic literature can probably pick up on it). Frow believes that all communication is precluded by genre; where here genre isn't like the industrial market segmentation, but a more foundational question of framing. We engage with material through frameworks that presuppose certain material are to be present with a certain quality, and that this quality should be engaged with through the framework - something that aligns a surprising amount with the concept of genre, except genres aren't umbrellas materials sit under, but rather multiple frameworks (material never has one genre, rather it uses many). The idea that things should be divided in genres in the sense of Spotify or bookstores is an industrial practice and mostly a shorthand, not really reflecting how material actually works. There are also a multitude of genres that are not part of the industrial environment, such as conversation, which is further subdivided into stuff like family conversations, forum posts, Instagram DMs. Genres this way don't just presuppose aesthetic effect, but construction of meaning.
Basically, whether material is succesful depends on whether it is properly framed and engaged with through your understanding of how the material works. If I listen to a rock song, I know its structures somewhat, and the material engages with my understanding of it. I can also engage with a material deliberately by misappropriating a genre the material creator didn't intend, and sometimes it works. Frow does a thought experiment early on, reframing a crap newspaper clickbait-esque headline, and trying to read it as a poem (although he does a mistake of praxis by adding a line durnig the experiment), noting that it also works well as a poem, and that basically everything in it changes inference and meaning.
Man, I went on longer there than I should have. There's more detail in the book. Better phrased than me, too, as always, I'm rambling.