I have a slightly different view. To me, it comes to a fundamental divide about how one views D&D as a game, and the role of the DM. Upthread, you see a lot of people talking about "generic" campaigns, and how the DM must explain all their decisions in detail. I don't think that should be correct.
Unless you're in an officially sanctioned event, the DM is running a specific campaign. And this is where the divide starts. Many players believe, perhaps with good reason, that anything listed in the rules (whether it's the PHB, on-line UA, periodic WoTC pubished materials, and so on depending on the player) is "fair game," and so long as they are playing D&D, the DM cannot disallow a character choice unless the DM articulates a reason that is "good enough for the player." Disallowing a race, or a class, or something else is tantamount to the DM saying, "You know, a long sword only does d6 damage." It's against the rules.
I feel a little differently. To borrow a phrase from employment law, a DM can make rulings for a good reason, a bad reason, or no reason. Let's use gnomes as an example. The DM could disallow them because gnomes don't exist in the campaign world (good reason). The DM could disallow them because he tripped over a garden gnome when he was 6 and broke his arm, and has forever hated gnomes (bad reason). The DM could disallow them, because (no reason). No matter what, there are no gnomes.
This, of course, is where the social and collaborative aspects of D&D should come in. The DM and the table should be talking- openly and honestly about things. There should be some level of mutual respect. A player should feel comfortable making a request, and justifying that request. But people have to learn to accept "no" as an answer. If you can't accept that - then maybe you should be the DM, and not the player, as you clearly have very good ideas as to how to run a game, and you should put them into practice.
I say this not to be snarky, but with humility. I have seen bad DMs in action; to be completely honest, for my first year of DMing (because no one else would) I *was* a bad DM. And there is little that is worse than to feel trapped at a table with an inconsistent DM who is making rulings for arbitrary reasons without any explanation. But if the DM is that terrible - then walk away. I say this not because it is "easy," but because that is every player's right if they are no longer enjoying the experience. But many DMs (such as myself) started because they were at a table with a bad DM, and went to form their own group.
Which is what this should boil down to - everyone having fun. And part of that is trust. There are excellent DMs that have severely restricted choices for players, and there are terrible DMs that allow a player to create whatever they want. Either you have a good DM, that you trust, or you don't.
Tried to find a place to snip and save space, but honestly I agree with you in the practical sense. No amount of philosophizing or arguing is going to change peoples minds once they are set, and I am looking at this from a "generic" perspective, simply because you cannot possibly cover all possible examples and worlds.
I also don't disagree with worlds having specific restrictions. For example, there are no Half-orcs in my games. Instead anybody playing what would normally be a Half-orc is simply just an Orc. I did not come up with this restriction though. One of my players brought up to me that he was very uncomfortable with the implied half-orc origin and I decided to change it. Luckily the Half-Orc player I had was completely on board with it and we loved the new concept. I just kind of kept it going since then, though different world different reason.
Well, besides 'not liking them' because I don't think they add much of anything to the game that couldn't be better done with a human (which, in full frankness, would be how I'd anticipate a player would actually play one), the basic problem is that I can't see how they'd integrate with society. Most NPCs would take one look at a tiefling character, and decide they'd better burn this monster at the stake before it started eating their children or something worse. I feel that it would be utterly disruptive, and is really only appropriate for a 'Planescape' or science fiction style campaign were gonzo weirdness is the norm - not one on a generic vaguely medieval/early modern gritty fantasy world. And if you really wanted to play something with fiendish heritage, that option is open just in not quite as blatant and pitch-fork mob provoking of a form - and even then I'd probably caution you against the ideo until you'd proven to me you had the skill to pull off such a difficult concept without wrecking the fun of everyone else in the group.
Two points to this I suppose.
I can accept your reasoning for Tieflings. In a game where the world is more dark ages and fearfully superstitious I would agree that character would cause a lot of disruption. However, if that is the reason you give me and then it is not reflected in the game world, that is going to strike me as quite odd. After all, the wizard or dragon sorcerer could just as easily be burnt for practicing dark magics or looking different. Human villagers would be quite hostile to elves and dwarves for being different and strange. It becomes a whole package.
Second, while I completely get the line about proving ones skill before being allowed to try disruptive characters, it simply rubs me the wrong way. I even agree with it, it just seems like bad phrasing to me
Because gnomes don't exist in my world, so the package isn't there. And in particular, you'd be trampling all over established norms of my setting, including campaign secrets players aren't supposed to know but to perhaps discover during play. You could play a character with the personality of a Gnome and largely the abilities of a Gnome, but it would be a Sidhe of a somewhat peculiar nature (but that's ok, because don't they all?).
We seem to be speaking from different perspectives on this point. The package of "Gnome" does exist. I can point to it in the PHB. My point was a player asking to play a race may be asking for the entire deal, not just a series of personality quirks. That isn't to say gnomes look the same or act the same or even exist in your world, but a gnome is more than a "fey-based trickster with a love of small animals who stands under 3 ft tall". It can be reduced to that point, but reducing by it's nature loses something in the process.
I get that is why you are asking the question you are asking, but if you're going to custom tailor something to fit what they need, is not usually simpler to just let them play a gnome?
Now you are no longer pitching just a character to me, but an entire pantheon, the associated cosmology, a mythic story, and indeed broadly the setting of the story. Why should 'the Gnomish pantheon' exist? I don't even know who the "Lost Sisters" are. To me this is like saying you want the next campaign to be "Star Wars" so you can play a Jedi, and if the campaign isn't Star Wars that you still want to be a Jedi because you are fascinated by midiclorians and have a great idea for a character that explores that concept. Ok, playing a Star Wars RPG is a reasonable desire, but then it bloody well ought to be obvious that the GM's desires and personal tastes do reasonably matter with regards to what he runs if you are dictating setting to him. If I didn't like Star Wars, you shouldn't expect me to run a Star Wars game just because you do. Why in this case would you be remotely taken aback by the DM's answer that he doesn't like such things? Or why would you even be taken aback to hear that though you were running a Star Wars game, the DM didn't like midiclorians and they weren't considered canon within the game?
In playing a Gnome cleric, to me, that means I should look at the Gnomish pantheon. My characters actual religious practices might change slightly (this particular gnome is actually part of a "cult" and focuses on worshiping the entire pantheon and the idea of community instead of a single diety, and of course "community" could be covered by any number of other deities if I absolutely needed to), but this brings me back to what I was saying above. A player picking a race may be wanting more than simply a body structure and stats. Gnomes have gods and culture and everything that comes with it. For me personally, choosing to play a race (and especially a class like cleric which ties so deeply into that) means looking into what all of that will mean.
And, honestly, saying I want to play a Gnome cleric worshipping from the Gnome Pantheon in a DnD game is more like asking to play a Jedi with midochlorians in a sci-fi game that includes jedi and midochlorians as options than asking to play a Jedi when approaching a DnD game. Now, if you decided your world was more Star Trek than Star Wars then obviously my concept does not work, but if we are playing Star Wars and the DM says he hates a wookies and therefore wookies don't exist then I would be surprised. If he said we're playing 200 years in the future and all the wookies were killed in the war, so I can't play one, that is more understandable.
What I think we're talking past here is reasonable expectations. If I come to a table expecting everything in the PHB to be allowed, and then I'm told things are not allowed, that is going to raise my eyebrows. I can't say I wouldn't adapt to your world, simply that if I came to the table with a set of expectations that was reasonable, I might try and understand the reasoning of why my concept was not allowed.
But 'advantage' is an attribute of 5e D&D. And that's fine, we may be playing 5e D&D, but how you get to the idea of "highly resist to mental magic" is entirely system dependent and ultimately a bit arbitrary. There is generally, even within a system, more than one way to get there and certainly if we are playing GURPS the mechanic for 'highly resistant to mind altering effects' can be different. Now, you might not like GURPS mechanics generally, but that's not the same as saying that the concept isn't provided for in the system. If you come to me and say, "It fits my idea for the character that they be highly resistant to mind effecting magic.", then we can discuss how to mechanically implement that idea. I'm ok with the idea. But whether we implement it as +3 bonus on such saves, or as 'advantage', seems to me to be of rather less importance.
There is nothing wrong at all with marrying mechanics with your background. Indeed, I encourage such things in my own rules. But whether, "Raised by wolves" is implemented by taking the Feral trait, or by Unusual Background, or by being an Outsider or having the Profession Primitive or however a particular system implements the idea mechanically seems to me a thing of rather less importance than having some mechanical marker that distinguishes the character from ordinary ones on account of the unique background.
I was talking about how the mechanics informed the concept. I remember (sub-teacher typing during plan period, so brain is mush) that someone asked "Why are you pitching mechanics and not a character concept?" My point was that they can be one and the same. A person may want to play a Goliath not only because of their strength bonus and damage reduction ability, but also because of the lore and thematics of the race. These things can be separated, but if a player wants both, then seperating them might not make things better.
You are putting the dividing line in a different place than I am. I do see a stark divide between, "I want to be good with a sword" and how that idea gets implemented mechanically by the system. There are all sorts of different system mechanics for implementing, "Great swordsman". When a player comes to me with the concept, "Great swordsman", I'm happy to oblige and point you toward system mechanics for implementing that idea. But I'm not necessarily because I'm happy to oblige the concept going to allow you to play a multiclass Factotum/Kensai/Duelist with Robilar's Gambit because you've got an infatuation for those particular mechanics. To me this goes beyond marrying mechanics to background or concept, and starts to fetishize particular rules.
Likewise, while I'm normally happy to let the player invent a certain amount of Lore for their backstory, up to and including working with the player to invent organizations or even deities, I'm not necessarily happy to import some other DMs existing canon into my world. If you start deciding that you just have to have FR, or Dark Sun, or Krynn or Greyhawk lore, races, deities, and organizations on Korrel, I'm probably going to tell you to go find a DM that enjoys playing on some other DM's world.
"No, I was planning to run a game in Sword Coast region of Sartha on the world of Korrel - there are no Kender, and Minotaurs don't ever walk around the street like they were ordinary persons. And, yes, you can worship a deity of justice and light, but no, you can't worship the Platinum Dragon." or "Actually, this game is going to take place on a giant gas world were stone is very rare and precious, and people sail about on flying ships, and no PC elves of any sort are allowed." Why should this take anyone aback? Why indeed would anyone assume Minotaurs, Kensai and even Tieflings were normal?
Until they have sat down and heard about your world, then they must make decisions based on assumptions. If you say you are running a DnD game, and a player is really excited about playing a Tiefling Warlock because they know DnD and see those options in the PHB, then they have no reason to assume that will not be allowed.
The time line of the discussion is important as well. I'm thinking of a player approaching before session zero, and the DM's world not being presented until session zero. This is in the large scale of things a minor issue, and perhaps I'm making a bigger deal than it will ever be, since I suspect I'm a little defensive on this issue. It's just something I've seen discussed a lot.
It is because of the demon lineage. One, I am not interested in including a race of people with a demonic lineage. Second, when Tieflings are part a campaign that I run, their role is going to be along the lines of Damien in the Omen series and similar 70's occult films not Marvel's Son of Satan, the half-demon from the Supernatural series or even Sam Winchester (although Sam only had a demon bleed into his mouth as a baby). It is not in a matter of nature vs. nurture issue. It is strictly nature. There is no free will in that scenario. The character is Evil with a capital E and I don't allow evil player characters.
For me, that's a big leap. I don't see Tieflings as being that close to Demons. To take this into the realm of chemistry and medicine for a second, I can accept Demons as being uranium (pure evil by nature) with no problem. However Tieflings are not a smaller piece of plutonium, they are the result of the "decay chain", closer to Bismuth. Dangerous and connected to the radioactivity of their ancestor, sure. Defined by it, no.
You see Tieflings as being different then okay, but nothing about them tells me that they have no choice between good and evil.
And, my answer would be that the campaign already has a pantheon (I create one for every campaign). It applies to all of the races.
As a personal tangent, That is the complete opposite of my homebrew. My choice was to have all the gods belong to racial pantheons, with the ones "unclaimed" meaning they defaulted to human, as most DnD products have a human bias (shocking, I know). This led me to stating my humans are by far the most religious of all the races, seeing as they have so, so many gods and goddesses to choose from.
It is an interesting choice, just the exact opposite of the route I went.
