I actually think there are 3 core definitions of MMI in this thread. IMO there's also been quite a bit of conflation and jumping from one of these definitions to another mid discussion.
- MMI is a criticism of the reliance on DM adjudication for PC action success/failure present in some RPG's.
As you note above, those that enjoy and play such RPG's don't find that this definition of MMI describes their games. The children's game MMI is about asking permission, but that's not present in such RPG's as the games don't actually give the player the ability to ask the DM's permission. Instead, these games only grant the player the ability to declare actions. IMO, the conflation of 'declaring an action' with 'asking the DM's permission' is the easily seen failure point of this criticism.
- MMI is strictly certain dysfunctional state(s) of RPG's reliant on DM adjudication for PC action success/failure.
IMO, whether everyone adopts this definition of MMI, we all agree that reliance on the DM for adjudication of success/failure can factor toward dysfunction at some tables. Thus, I don't think this definition is invalid. It just lacks explanatory power for what we are seeing in this thread. If MMI was really primarily about something external to a player then we would expect to see broader agreement around the external situations where it occurs. We don't see that though. And it's not just around 'sides'. There's significant nuance and difference of opinion on many examples, even from those whose core positions mostly fall on the same 'side'.
- MMI is a player's feeling of needing the DM's permission to do something in the game.
I believe this is the best valid definition of MMI based on the full context of this thread. It explains why there are such differences of opinion around what gets called MMI by various posters. It explains why all objective definitions fail to reach any kind of consensus. It explains why we can have non-dysfunctional play examples that still get called MMI. IMO, this thread is exactly what we could expect if MMI was really about the player's feelings and their individual interaction to external circumstances.