OK. Now, what about: "one or more of these choices does not fit in with the game world as envisioned and-or designed"? Example: if in my world the Gnomish culture as designed (and clearly stated upfront) says only female Gnomes go adventuring and an adventuring male Gnome is likely to be scorned (or worse) if it ever encounters any other Gnomes, do I allow male Gnome PCs or just ban them? And if I do allow them, and the scorn comes, is it then a "don't say I didn't warn you" moment?
In other words, is it wrong to make some PCs culturally or racially harder to play? Some classes (Assassin being the most notable) are already similarly harder to play, by comparison.
As can the philosophy "limitation breeds creativity".
At the start of my current campaign all PCs had to be a) Human and b) of the same ethnicity (Greek-equivalent). I did this intentionally, to set an early tone of what sort of culture the game would be set in and to drive home the fact they were starting in a place where non-Humans weren't always very welcome. What this meant was that if someone had their heart set on playing an Elf right from puck drop they were SOL; they'd have to wait a while. Is this wrong?
Lan-"as soon as the party got out into the field and started turning over characters (at a frightening rate!) I opened it up to other races and ethnicities more like a standard game"-efan
So I'm actually going to pick this one up and try to think aloud about it, because it's a really good and interesting question. I've built a number of cultures that have very aggressive gender norms for both fantasy and science fiction gaming, and I've found them to be very interesting and rewarding to play around with. But they can be very problematic for a few reasons, so I think it probably is helpful to approach them with caution, especially in how you introduce them to players.
Lessons learned from my experience, if what you want is to do art without running off players:
1)
Designing against the default social expectations of your own society is helpful. Probably the best and most useful bit of design I did in this vein was for a sci-fi game, where I started from Asian cultural tropes (especially Japanese, because I was familiar with them) and set up a matriarchal society with a slanted birth-rate (more women than men) that embraced bisexual polyfidelity as its its default family model - two to three women and a man as the default household, with one woman traditionally acting in the military sphere, a second as the primary parent and the third in politics/business. The man was very much seen as a valuable resource to be cossetted and kept from doing anything silly and reckless like joining the Star Navy or taking a stressful job - artistic careers and helping professions would be much more in line with his family's needs.
So what did all of that get me? It threw all sorts of default assumptions about life into relief for the players, who were mostly playing outsiders interacting with this culture, and gave them a chance to think about what a very different understanding of things like family, gender roles and gender expectations might look like. It made for a very memorable and striking culture that people seemed very intrigued by. And it got me well away from the kind of reminders of day to day oppressiveness that, say, a hidebound patriarchy of the sort we see all the time in fiction might evoke. This was a culture that was different enough to intrigue without invoking the actual daily problems of people's lives, and that was valuable to me and to them.
2)
Avoid universality. This is mainly a tip for helping to avoid alienating players, but it seems to help a lot in making setting design more lively and flexible, too. Avoiding statements like 'all dwarfs believe' or 'all elves have these expectations' can get you out of the trap where the carefully detailed culture you've built up for your game doesn't mesh at all with the expectations of your player(s). In those situations, being able to say "The gnomes of Region X are a rigid matriarchy with these certain practices, but the gnomes of the High Mountains have a very different view" can really open up options. Even better is if you can sit down with your player and do some cultural design work on the idea they have about gnomes/humans/elves/whatever, so that when their character runs into your carefully designed culture, they can respond the way many humans have in foreign countries all through history - with wide-eyed fascination that so many things can be different between people who are so superficially similar. And it really takes pressure off of you in terms of cramming an awkward character concept in - the players who love to be inspired by the setting can draw from your prebuilt cultures, and the ones with firmer ideas can be accommodated (within reason) without disarranging your work too much. So while I don't think that your "all players must be human and from this region" campaign is
wrong, per se, I do think that you're asking for a great deal of buy-in from your players up front and I hope you talked about it with them before hand (and, if you didn't, that it managed to go well anyway). That sort of planning can look great on paper and
be great with collective consent, but it can also cause a lot of friction if there's not deep trust and familiarity between the group and the DM.
3)
Don't punish in an arbitrary way, especially when people know your views. Most of my players know that I can be a bit of a misandrist - my life experiences with men have not been fantastically positive, and that tends to affect my gut level response to them. With that in mind, I try very hard not to put my players in a position where it feels to them like I'm punishing them for deciding to play a male character of a particular race/class/etc. I will go further out of my way to accommodate them in that regard than I might normally, because I'm sensitive to the fact that my first impulse when someone wants to play a female character is "great!" and my first mental reaction when they want to play a male character is "Another one?" If you're running for a diverse table, this kind of self-awareness and a willingness to try to ensure your creative work doesn't resemble a personal soapbox can really pay off.
So "wrong" is a strong word for any of what you're talking about, but "likely to cause you and/or your players problems" is definitely a phrase I might use.