I think in classic D&D, it's quite frequent to step back from character to some degree and try to reconcile X to Y. I think that "not roleplaying" (your phrase, not mine) refers to not seeing X or not caring about X relative to Y.
<snip>
So I'll infer that "less immersion" is when the player is primarily motivated to do Y and doesn't have any X in mind. I think that's when the danger of "dissociation" feeling comes in.
<snip>
I feel like I'm doing "less roleplaying" when there's a whole lot of Ys and a whole lot of glossing over the Xs.
Using the terminology that I posted
here, doing Y without having any X in mind is
pawn stance. Arguably, that is when RPG play has started dropping away and board game play has commenced, though it will depend a bit on the details. Deciding to join the party, in D&D, is perhaps best seen as part of the set-up rather than play itself. And in many games that involve strong GM force, taking the GMs adventure hook (which often involves pawn stance, or the thinnest veneer of PC-motivation-rationalisation) is also best seen as part of the set-up.
But constant pawn stance once the scenario is in motion can definitely be an issue.
But what Justin Alexander is complaining about is, as far as I can tell, not pawn stance. On the player side, he seems to be complaining about director stance, or about mechanics that don't involve stance at all (eg because they're pure metagame and don't have any direct bearing on the content of the fiction - rolling for initiative would be an example). On the GM side, he seems to be complaining about mechanics like the War Devil's Besieged Foe:
Minor action, at-will, a target within line of sight is marked by the war devil, and allies of the war devil gain a +2 bonus to attack rolls made against the target until the encounter ends or the war devil marks a new target.
I've never played M&M, but I understand it has a mechanic whereby the GM can introduce a complication that adversely affects a PC, but to do so must give the PC a fate token. (Other games have similar mechancis). Besieged Foe is capable of being interpreted in a similar way, as a pure metagame mechanic: when the GM has a War Devil on the table, s/he can complicate things for the PC - the PC becomes "besieged" because the allies of the War Devil get a bonus to hit him/her, while s/he (due to being marked) has a penalty to hit anyone but the War Devil - but the trade off is that, to do this, the GM has to expend a resource, namely, a minor action from the War Devil's action economy.
Alternatively, Besieged Foe can be played as a "fortune-in-the-middle" effect - when the War Devil uses the power something happens in the fiction (a curse, a command to allies, etc) but what exactly that is has to be narrated on a potentially different basis each time the power is used. Played this way, the power would be similar to the Baleful Polymorph I described upthread, where my player narrated its duration as reflcting his god's freeing him from the effect.
However Besieged Foe is played, it is not an issue of stance. Nor of "Xs without Ys". Justin Alexander's concern seems to be that there is no provision for fictional positioning - but if the power is played as fortune-in-the-middle that's not true (some fiction will be narrated), while if it is played as pure metagame than that's not a problem. In M&M the player can't leverage fictional positioning to stop the GM to introduce a complication either, because the event is not one in the fiction - it happens entirely at the metagame level.
Unless we know the personality, motivations, goals, etc. of the character being played... the action of swinging on a chandelier can't automatically be proclaimed as author stance as opposed to actor stance.
Agreed. But I think Hussar is correct that it often is - that players of fantasy RPGs often have their PCs do things because they're cool, rather than because they're "in character".
Your experience may differ, of course - all any of us can do here is try to generalise fairly from the experiences we've had.