If you think you are having no default mode activity, you are likely fooling yourself. It is externally observable when humans have a quieter default mode, through subtleties of behavior, one can notice a calming presence, like that of non-linguistic animals. Even without language, default processing loops can be quite complex, not even taking into account multiple diverse parallel processes. Inner dialog can be very useful. Not having inner dialog is not stupid. I agree though, that in many situations, or for some people, default mode inner dialog can have a debilitating effect. But in an evolutionary way, thinking "I can survive" in a perilous situation, likely outweighs thinking "wtf I am I doing w/ my life?" when sitting on the couch. But consider the evolutionary effects of the modern externalization of inner dialog through devices.
> But in an evolutionary way, thinking "I can survive" in a perilous situation, likely outweighs thinking "wtf I am I doing w/ my life?"
My hypothesis is that the inner dialog genes proliferated by providing higher status. People with an inner dialog are more likely to be charismatic, entertaining, etc. because they are constantly practicing without knowing it. Think the prehistoric version of a big account on twitter. I can't imagine it's possible to become a successful writer, elected politician, or a war general without having internal dialog genes.
The externalization via devices will just magnify this effect.
Whenever something is highly selected for in isolation, there tends to be a long tail of unforeseen consequences. (See: sickle cell.) Some people will have too much of it and end up with some type of schizophrenia or schizoid state that puts them in fake dream worlds. If you get a lot of these people together in a room, you could make them believe some crazy stuff with the same conviction as ours in gravity. (How religion started?)
