Yes. I would be ok with working out something that looks like a thiefling and works like a thiefling. That still isn't a thiefling. You are still limiting away part of the defining lore. How do you know it is not this flavor the player is interested in? I would indeed find that incredibly more likely than that they just want to play something with darkvision and horns.
You don't know that though. You can't. Because, again, there are a zillion reasons.
I have a player who plays (but is on hiatus) a tiefling. Said player does not care about the
hell stuff in the least. It's purely the aesthetic, and to a certain extent, the distance between the character and the rest of the world that that aesthetic induces.
And what put me in the position to be the one to permit it, if it wasn't my authority as a GM? And I though it was this authority as a GM you sought to (severly) limit. So if you remove the GMs ability to make lines, who is then in a position to not permit something?
You have not just put in an assumption unsupported by what I said. You have outright
ignored what I explicitly said, and which you had previously quoted and replied to.
Remember, I both said
limited bright lines--so some, but not free rein to do whatever one likes indefinitely--and specifically said almost surely
more than any of the players, and probably even more than the players
combined. The only way that could be true is if they have that power, and the number is (for example) greater than five (presuming five players and just one allowed "bright line" for each player). In other words, my explicit words indicated that the only possibility is that they have that power. Why would you think I meant them to have no such power at all, having specifically responded to the post where I said these things?
Yes, indeed there are. You know how munchins, murder hobos and certain kinds of power players have a bad reputation? I am of the belief that with aproperiate constraints and nurturing players that would otherwise have been inclined to drift in these directions could indeed be a lot of fun to play with. I do not like the idea of excluding someone from the hobby if there might be known accomodations that would allow us to play well together.
You know how there are "DMPCs" and "killer GMs" and certain kinds of power GMs have a bad reputation? I am of the belief that with appropriate constraints and nurturing, GMs that would otherwise have been inclined to drift in those directions could indeed be a lot of fun to play with.
The scythe cuts both ways.
I struggle a bit with getting what you are trying to say here. I think I agree in the spirit. I am just not sure how it look like in practice.
Let me put it like this.
Stealing things from your parents is bad.
Listening to Nine Inch Nails while your parents are trying to relax after work is also bad.
I think it is very, very unwise to treat the first idea as being precisely the same kind of thing as the second. It turns "Do not steal" into a mere
preference, rather than a basic and fundamental rule of behavior that people should follow (barring extreme extenuating circumstances etc., etc.)
Instead, "Do not steal" should be treated separately and much earlier. It is part of the bedrock foundation, something that needs to be established in order to
have a family unit that functions and can support its members.
After that "this is the absolutely essential bedrock of having a family" step is established,
then we can set the bright lines, which are based on preference. That doesn't mean the preference-based ones should be ignored. But it properly emphasizes the difference between the two restrictions. Some things are restrictions in order to have a foundation to start from. Other things are restrictions for...call it "daily life" within that built structure. If you don't like the NIN example, replace it with something like "tracking mud all over the house" or whatever else, something that clearly causes problems, but also isn't on the same fundamental-bedrock level as "Do not steal".