As noted in my tossed-together example, the PCs had already adventured close to those hills. A player (or me as GM) post-hoc putting a Dwarven realm there retroactively changes the parameters of that adventuring. Thus, as GM I wouldn't do this but in your scenario am I allowed to stop a player from doing this?
In that example, why would you add something to a region that doesn’t make sense based on what’s already established? I’m not saying that contradictory things should be added to the setting.
What I’m saying is that (to lean on the examples you’ve provided) if you let one player craft the lore of the dwarves, and he decides they’re beardless and are clannish and somewhat barbaric, and then a later player wants to play a Tolkienesque dwarf, it’s bot a problem. You just add a more traditional dwarven culture somewhere else in the setting, where it would make sense to do so.
Not determining all this ahead of time need not cause contradictions. It also allows for player input on the world, which usually enhances engagement and also variety of content.
Your concerns about it aren’t accurate. Just as we don’t know of Rivendell or Fanghorn until they are introduced in the story, it doesn’t cause disruption. We can learn these things as we go.
Not so bonkers. If something unbalanced arises out of sheer random chance I'm fine with it. What I don't want it that it be player-selectable.
Yeah, that’s bonkers. The noble character is either an issue or it’s not. If it wasn’t an issue in your game where it was rolled, then it’s not an issue in my game where the player selected the noble background.
This is what doesn't make sense to me. I can be friends with a fellow player, respect them. But they can be running a PC I don't care for. As long as they aren't being completely disruptive and destroying the enjoyment of the game for the other players, why do I care? As a GM what could I do about it and why would I care?
There are certain social contracts we abide by when we get together to play games. Whether that game is D&D or Pandemic, we treat each other with respect. Beyond that? I can't even imagine. Which is why I keep thinking I'm missing something.
Well as part of a group activity, where the spotlight may shift to other characters from time to time, I prefer that people care about the characters. That they’re interesting enough that other folks don’t check out when play focuses on one character.
It usually also implies that some amount of creative effort had been made, which I appreciate and which possibly inspires others to contribute likewise.
It kind of creates a positive feedback loop where everyone cares, and then everyone tries, which makes everyone care more, which makes them try harder… and so on.