A DM that has created a world where all such things are fixed is a DM that isn't actually interested in accepting player input. That's literally what I've been arguing, repeatedly: the DM that fixes so much of the world that the players can't ever touch or change or even question it.
That is a good way to phrase your argument. Thanks. It is clear. I mean, I understood it before, but this crystalizes it.
I would defer on the touch, change or question. I do not know any DM that wants a still-framed world. They want their players' characters to interact and be able to change the world. They can touch it. They can change it. But, they do that during the adventure with their PC's, not by choosing a race during character creation.
Here is what they can change during character creation: where certain backgrounds exist, where a race can grow up, what occupations might exist in specific places, and even smaller enclaves of cultural shifts.
Here is the one thing these DM are arguing they can't change: You can't be these other races, you can only be these 4 or 8 or 12 or 16. That is it. I do not see them arguing any other thing in the world that the player can't change.
Like, is this really a thing? Do DMs really fix the "races and politics and interactions" so frequently? I thought the whole point was to play to find out what happens. What's the point of being a player in something where the DM has pre-figured so much of the world? I honestly don't feel like it would be hyperbolic to ask, "Ah, and is the DM setting the players' alignments and favorite colors, too?"
Again, they do
fix things. That is how any story starts. Ten Towns has a curse on it, it is forever winter here. Xonthal's tower has kept the villagers around it safe from marauding creatures for many years. Saltmarsh is on the sea and houses many fisher-folk. The savage frontier is a place where hill giants are storming villages and gathering all the sheep, cows and grain that they can.
I do not feel like it would be hyperbolic to ask can a player understand that these settings are in place, so please work with them. If not, maybe it is a lack of imagination on the player's part, not the DM's. If that is the case, then the DM can sit down with the player and help them draft something that they would be happy with. If at the end, if they are only happy with being a mermaid from under the sea, then perhaps discuss a different game run on a different night.
And, yes, one-offs should be perfectly acceptable, if a player is looking for something particular. Just as the DM should listen and consider, the player must need to accept a spectrum of answers. If the player isn't satisfied, maybe it just doesn't work. If even a one-off is a problem for the DM, maybe it just doesn't work--but at least giving the player the time of day, letting them talk and honestly considering the possible options--doesn't seem like it's this horrible offensive thing. It doesn't need to
Agreed. A one off should be open as open can be. Because, in the end, it doesn't matter. You are not investing hundreds of hours into prep time, spending hundreds of dollars on materials, and/or building close, and maybe lifelong bonds with people.