We have various folks who ask D&D lore questions, and they get forced to pick a setting in the same way we force people to choose a rules edition, or have their question closed. In the history of the Forgotten Realms, has a Nightmare ever been cleansed of evil? is a recent example.
From a certain point of view, this makes sense - settings are different, right, halflings only strap you to the feast-stone in Dark Sun (unless you really deserve it otherwise I guess), so doesn't that stand to reason?
Well, here's the problem. D&D itself - across its editions - has NOT been clear about maintaining that division. Even the "core" races, religions, etc. in the Player's Handbook form a sociology and mythology that some settings trump but do not require a setting to define. The majority of older Dungeon Magazine articles about the ecology of this or society of that, for example, were not labeled for a specific setting like the Realms or Greyhawk, but were just "generic" setting content.
This had been bothering me for a while, but I came to this realization after listening to a recent Plot Points podcast that discussed this commonality and being led from there to the new Mordenkainen's Tome of Foes where they explicitly talk about items in the "D&D Mythology," a continuing mashup of things from various worlds (or that were generic in the first place, like the demons and devils). Drow being the children of Lolth etc. - while there are settings that override that, it's not a "Greyhawk" or "Realms" or whatever thing, it's a "common across many D&D settings thing." The Dragon Mag "Wizards Three" articles with their Wizards Three (representing Greyhawk, the Realms, and Dragonlance) gave an imprimatur to this whole multiverse mash-up effectively utilized by, I would dare say, the majority of D&D groups over time.
So just like we can ask GM techniques questions not specific to a specific edition of a specific game, or use system-agnostic, because while games differ there's lots common to all trad games, for example, do we need to command questioners to specify a setting at the risk of question closure?
If they are using a specific setting, then obviously they should mention that. But that's not how many people play D&D. D&D is often played as a partially made up mashup of whatever books and adventures and ideas people have at hand. Is it really in anyone's best interest for them to be forced into "uh... in the Forgotten Realms I guess?" Does that solve their problem?
Given this, how should we provide guidance on D&D lore questions?