I don't think anyone is suggesting that social conflict rules are useful for deciding whether or not NPC farmers with their wagons give D&D-style PCs rides in the direction they're going anyway.Well yes, obviously, I decide. But it's more like, if the PC's are reasonably well-mannered and ask an NPC for a ride on their wagon to a place they are already going, and the NPC is at least neutral, no roll.
But isn't that how it's supposed to work? The DM decides when rolls are necessary?
That seems pretty low stakes.
But the example that has been discussed in relation to "no doubt" is not that. It's Faramir ceding rulership of Gondor to Aragorn. That seems pretty high stakes to me.
I think the general proposition "the GM decides when rolls are necessary' is not helpful here. How does the GM decide that. Following what principles?
If the GM's principles are I decide in advance - or in the moment - how any given NPC might respond to any given proposal, then no rolls will be called for and no social conflict framework is required. That's one way to do it. (Of course, we could do the same for combat, but typically don't.) But it's not the only way. Heck, back in 1977 one of the earliest RPGs, Traveller, had a whole range of subsystems for resolving social encounters involving police and other officials and bureaucrats - Admin skill, Bribery skill, Streetwise skill, etc. And also for resolving social and emotional situations involving military or quasi-military recruitment and command, using Leadership skill.
Interestingly, and at odds with some D&D traditions, Traveller uses non-random methods for Leadership skill - at various ranks of Leadership, soldiers simply follow commands with no roll required. But uses random methods for dealing with public authorities - which is to say, the game is oriented around dealing with bureaucracy as a high-stakes situation! That may or may not be to anyone's taste, but that's a decision about aesthetics, not a technical consideration in game design.
Which all goes back to my point: we don't decide the scope and workings of a social conflict system by working out what is uncertain. Rather, we decide what we want to matter in our RPGing, and then build a social conflict system around that if we want to.