I did a poor job in my initial post of framing my argument, and most likely should not have used such a loaded term which can be a great many things to a great many people.
What I'm arguing is that we could have more successful gaming if we were just as mindful of social dynamics at the table as we tend to be of the fictional situation. The way I see it few character concepts are so nailed down in stone that there is only one possible way they would approach a given situation. I'm suggesting that if James is having a rough day and wants to pound some orc faces in it might be helpful to have Demarius, your elven wizard issue a word of caution, but play out the encounter with the orcs rather than negate James' wishes some times. I'm suggesting that if establishing trust with a new PC is an issue playing out an extended series of wary glances might be more fruitful than stonewalling the game. That's the sort of thing I had in mind.
Okay, so it does sound similar to the example I asked about, then. ("I know that everyone would have more fun right now if I stopped pursuing this thread, because it's taking up a lot of spotlight, and I've had it for a while. I can see [James] losing interest. So, even though my character would continue to look into it himself, I'm going to ask an NPC to look into it for me so that everyone else has a more enjoyable time.")
I think that can be useful, or very useful, depending on the table. My players have an agreement that we play in-character. So, that means that sometimes they wait while stuff goes down, sometimes they don't trust the new guy immediately (though we try to take care of that one as part of the new PC backstory before play*), sometimes we don't get into a fight for three sessions (like my last three sessions).
But I do think that these things still need to be addressed by someone, even if the players have an agreement. As the GM, if I see the others getting antsy because one PC has been on something for too long, I'll start to sum up stuff to push the game forward (but pacing is a big GM responsibility anyway, so nothing new there). If a new character is going to be introduced, I work with multiple players to come up with a backstory that works for everyone, and explicitly ask if things will work out if the PC is introduced as presented. If the players are looking like they want a fight, I encourage them to go get into one (or go look for trouble)! It's a sandbox, and that's on them, too. Sometimes the world brings it to you, but sometimes you have to go looking for it, too.
(However, that last point does touch on what Campbell seems to be saying. What if we're playing a sandbox and only one player wants to go get into a mindless brawl because his mind is fried from a particularly mentally or emotionally taxing day? Then the other players might want to exercise some of that meta thinking that Campbell was talking about and cooperate. And that's where it can be useful at my table, even if my players probably won't do that.)
*For example, I just had a good friend join after he got back from his 16-month deployment, and his character was a cousin to one PC (a cousin he grew up with, and was a confidant as a child). Both were from the same noble house, and the other two PCs have a Complication (a mechanical feature) that they both felt as if they owed or wanted to improve that noble house. He slipped into the party pretty easily, even as one of the PCs positions himself to make a play at taking the throne from the king via complicated birthright laws.