@pemerton, I sometimes get the feeling that when people are imagining social mechanics in other games that they are imagining social mechanics that operate in the style and manner of D&D style spell mechanics, hence how social mechanics are (somehow) "mind control." So when they imagine D&D with its spell mechanics
plus social mechanics, the further addition of what they regard as "spell-like effects" encroaches on that limited bubble of action declarations that the game affords them.
However, I don't think that social mechanics in these other games particularly operate in that manner. And it doesn't seem to matter how often we quote the rules of these other games for them to engage or criticize, they will be ignored in favor of this prior assumption that seems to by a carry-over from D&D that anything of this nature is or must be spell-like. Either you, me, or anyone else can point to the sheer latitude of player choice regarding these mechanics, even when their PC is the one affected, and it won't matter. These mechanics will be regarded as binding on their agency as either Charm or Hold Person.
I can't say, for example, that most of the discussed social mechanics operate anywhere near the level of agency-removal as say the Charm spell does. There is a LOT of player choice that often operates in the framework of these social mechanics too. It's not necessarily, "I won, so you must do as I say." It's often, "I won, so I get what I wanted out of this Contest and you don't. We agreed that your character now has the complication 'honor bound to serve their lord,' so how does your character feel about that? What do they do in response?"
Moreover, if we accept the contention that social mechanics and magic spells equally impair action declarations, then how many "action declaring impairments" will we likely encounter between these average games? Honestly, I suspect that D&D would have more on average, and I do suspect from my own experience with these different games that I will have less opportunities for action declarations in D&D than I would playing Dungeon World, Fate, Cortex Prime, or Blades in the Dark. One reason I suspect that D&D would have more is because of central it puts it in the framework of combat, monsters, saving throws, spells, etc. And the framework of D&D seems to generally view
affect (of nearly any kind) as a negative for the player character rather than something that the player character actively engages as part of the fiction or a challenge that they actively put themselves into. There is a completely different mindset when it comes to how some people approach D&D (and by extension, all other games) that sees any affect on their character as inherently adversarial and encroaching on their territory.
As it's come up in the Gandalf discussion, I'd also emphasize that I don't think anyone has an objection to game mechanics influencing the mental states and decision making of NPCs. That's the entire point of persuasion/intimidation/deception checks after all (though its of course up to the DM to determine the degree to which NPC are susceptible to such influences).
But does that include the heart of the PC hobbit named Pippin, who (I believe) was there too?