Both of these concerns strike me both ridiculous and a little insulting.
Calling my concerns ridiculous is a little insulting as a matter of cold fact, so maybe don't ask question you don't want answered, and then insult people for the answers you asked for? Don't ask for people's lived experience and then take a dump on it, eh? Also claiming my experiences are "insulting" to some unnamed, anonymous person is some pretty next-level stuff lol.
Are you like, insulted that I wouldn't play in your campaign or something? Surely you wouldn't want me to? There's not much worse than a player who really doesn't want to be there.
Why should they play something else? While I prefer a few other systems (e.g. Tiny Dungeon, Savage Worlds, Barbarians of Lemuria, and, occasionally Rolemaster) to D&D, some people don't want to learn and/or purchase other systems. I know other people that have similar experiences and, as a result, D&D becomes the compromise system for fantasy. However some of those same players not wanting to purchase and/or learn a new system (other than D&D) are fine with customizing the campaign by limiting options. Plus, D&D has a long history of house ruling and campaign customization to tailor the experience.
????
Where did I say "should"? This seems like it's based on you reading words that aren't there. I'm talking about my own preferences.
38 years and multiple all human campaigns later and I've never once seen this. This comment is pretty off base I think.
You say that, but I've seen it happen, multiple times, with human-only campaigns people are suggesting, IRL and on the internet. And the fact that you and Reynard seem so outraged and keen to dismiss it outright, even though it's my lived experience makes me feel like I might have struck a nerve, rather than being "off-base".
To be clear, I don't mean "that's what ur doing u racists!" or something, I mean "I guess you are planning on a single-ethnicity group of PCs from a single town" (or have done that before) and are alarmed that some people might find that a bit concerning.
I would have first guessed they were trying to play something historical that would have been roughly that way and didn't want the focus to be on the fact one PC didn't fit the setting. (Something set in Japan without Tom Cruise, or set in Scandinavia without Arak, or pre-Viking Americas without who knows what, or....). I guess I should feel lucky that I haven't played with folks who would have made me guess something unpleasant.
That's the thing though, isn't it?
This is D&D. From when I started playing it, back in 1989, it had a colourful and wild cast of species, races, cultures, ethnicities. The first settings I saw were Taladas, Spelljammer and the Forgotten Realms. All of them extremely diverse (and Taladas actually more "real"-feeling than Anaslon for it). Every party I read about in D&D novels was diverse-as-hell, at least in terms of background and species. Even outside of D&D, whilst LotR's hobbits may all be from one little town, they're mixing with a half-elf (in D&D terms), an elf, a dwarf, humans from distant cultures and so on. I didn't even run into the idea of an "all-human" campaign until it was mentioned in a setting book a year or three later.
So when I see "all humans" I narrow my eyes slightly, and I definitely want to know what's the goal. If it's to simulate some historical period, I'm probably out because that likely also means no/low magic (including magic items), no dungeons (per se), no dragons, and totally personal opinion, but I don't think any edition of D&D works particularly well for historical settings, nor would I pick D&D for a game definitely featuring little/no magic, dungeons, dragons, or direct equivalents thereof.
If it's "you must all be from this small village" I'm even less interested, because typically that does involve an ethnicity being specified, and as you point out, they don't want anyone outside that ethnicity because, for reasons unknown, they think the campaign would "focus" on them. I've never seen that to be true. If anything, the "one weird PC" tends to get excluded from stuff (which can equally be a problem, but of the opposite kind) rather than getting centered. If you ran The 13th Warrior as a campaign, Antonio Banderas' character would probably be excluded or on the edge of most scenes, not at the centre of them.
And it's not usually outright racism or bigotry behind "You must all be humans from this village" (which happens to be ethnically white), but rather the whole "Reject modernity, embrace tradition" nonsense that Tracy Hickman tweeted about. Which in my experience means the campaign is likely to be some sort of ham-fisted attempt to recreate Lord of the Rings or similar, at best, or at worst, some sort of attempt to "go back to the good old days*" when heroes were all muscular dark haired pale-skinned men who rescued blondes from swarthy wizards, or fighting off subhuman hordes (who curiously seem to all be non-white) with all the low-level but constant racism that implies.
I have played in all-human campaigns which were perfectly good, note, even a "you are all from a small village" (though there was no suggested ethnicity - it was a fishing village on a busy coastline so people could have been from all over). But I am pretty suspicious, and unless the campaign sounded fantastic and there was a good reason for it being human-only (that wasn't "this is a low/no magic historical campaign!")
* = NB these "good old days" didn't exist - not even Conan is really like that.