I'm prepared to assert that, to a certain extent, it is about a sense of exclusive ownership.
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I just don't think we can get from "having a set of gameplay preferences with respect to playing D&D" to "continually arguing against other people with different gameplay preferences getting more of what they want out of D&D" without a need or desire to have a sense of exclusive ownership over the game.
I've enjoyed your posts in this thread. In this post, I want to suggest an additional consideration that relates to some of what you've been saying, and also to
@overgeeked's OP.
To start, an example of "modularity" in a RPG, drawn from 4e D&D.
The core 4e D&D rulebooks set out the "tiers of play". This is an idea about the sort of fiction that is appropriate to PCs of different levels. Roughly, at low-to-mid levels PCs do heroic save-the-villagers and rescue-the-prisoners sort of stuff, and fight Kobolds, Orcs, Ogres and the like. At what the game used to call name levels, which 4e called Paragon, PCs save kingdoms, fight Drow and Illithids and demons and giants, and don't really need to worry about where their next meal is coming from. And then at epic tier, PCs travel the cosmos, deal with and sometimes fight Gods, seal the Abyss, restore the Lattice of Heaven, etc. The Monster Manual is written to support these tiers of play, in so far as it assigns appropriate levels to the appropriate sorts of creatures and NPCs.
The Neverwinter supplement mixes this up: it offers new monster stats, which are designed to compress the
story of the first two tiers of play (as per the core books) into the first 10 levels - so it gives us Drow, Ilithids etc which are statted out differently - at lower level - than in the core MM, and offers scenarios in which PCs who are
mechanically of the lowest tier engage in adventures that, in story terms, belong to the Paragon tier.
(I would say that 4e Dark Sun mixes up in the opposite direction, stretching the fiction of Paragon tier into the mechanical zone of epic tier; but the books is less over about this, and because the execution of this is probably a bit more challenging I'm not as sure that it fully succeeds.)
This modularity requires recognising that
what level a Drow is, or a lich, or an Illithid, etc, and how one stats it up, is to some extent arbitrary. It's just a gameplay device. Likewise on the player side of things: whether my fighter who can (to use 4e language) Shift the Battlefield (1x/day solid damage AoE with forced movement) or (to use 5e languuge) perform 3 attacks in a round is a
village saver (like Robin Hood) or a
kingdom saver (like Achilles) is to some extent arbitrary. Again, it's just a gameplay device.
But that aspect of the 4e approach (and the other aspects of 4e that underlie it, like the system of minion vs standard creature statblocks) was
wildly controversial. There are a lot of D&D players who are insistent that the game tell them what level an Illithid
really is (or how many HD it
really has), how many attacks Sir Lancelot can
really make in a single combat round, etc. The idea that you can just toggle these things around, to support different relationships between the mechanics of PC or NPC/creature build and the associated fiction is anathema.
The same thing applies to your suggestion about equipment. The idea that there is no
truth or
reality about what difference it makes if you have "shovel" written on your PC sheet under "Equipment" is anathema to some considerable chunk of D&D players. They are insistent that the game rules tell us what a shovel
really is in the context of the game.
And this, I think, is the source of some of the resistance to thinking about D&D as a game.