If the state of the game lore regarding Druids is clear from the beginning, and the player agrees to that lore (by choosing to play a Druid), then no, it is not poor DMing for the DM to veto the action (I would take the player to one side and reiterate the lore and the fact that they agreed to by choosing the class). If they refused to change their chosen course of action then yes, one option would be leaving the game. The other would be to start a new character, as they would not be playing a Druid any more.... but it would be a red flag hanging over their level of respect for the game.
I’m coming from a position where I don’t care what armor druids can benefit from. If its only leather, that’s fine. What I care about is player agency.
So what I’m not getting is why you would go to that much trouble to remove player agency when you could preserve player agency with a simple in-character consequence. It could even be, “You find yourself lying on the ground writhing in agony. You begin taking 1d6 necrotic damage each turn, have a movement of 0’, and the only action you can take is to remove your armor.” Now you have preserved the fact that druids don’t wear metal armor in the setting, without removing player agency. They receive an effect similar to what a hostile high level spell might impose on them.
The point here is that in 5E D&D “The players describe what they want to do,” and “The DM narrates the results of the adventurers’ actions” (D&D Basic Rules p. 4). The DM describes consequences of the attempt, they don’t decide whether the character can or cannot try something. This has been the implied rule of what an RPG is and how it works from the beginning.
Of course there are social contracts. If you are playing a pre-defined game of honorable knights in shining armor, and one player decides to have their character start going around murdering orphans, its just common sense that you say, “Dude, really?” and the whole group tells them to get with the program. And one might reasonably do that with Druid taboos if it was understood that was a thing. But there should still be in-world consequences for what would happen in-world if that taboo were broken. It’s not about getting around the mechanical restrictions, it’s about the fact that somewhere in the history of druidism a Druid has found themselves in metal armor for one reason or another, and what happened? If they “ceased to be a Druid” great! What does that mean? Do they become a dead former Druid, do they change to a commoner statblock, do they lose all supernatural abilities, or something else?
Regardless of the exact nature of in-world consequences, the presence of them supports player agency, even if the social contract for that campaign is that druid players won’t be testing them because y’all just don’t want to deal with it.
But the 5e PHB has a major fail (which is the point I’m making), in that it ***in this one place, and only this one place in the entire product line*** forbids player choice to describe an action (in this case, for a Druid to put on metal armor) rather than suggesting consequences. It flagrantly violates its own rule byforbidding players to describe that their character is attempting to do something the character is completely capable of doing according to what passes as physics in D&D Landia.
I think half of us involved in this debate would have nothing more to debate if our opposition would acknowledge that the PHB presented the Druid armor taboo/restriction in a uniquely poor manner.
