Yes maybe it is predominantly an Ni vs Ne thing? That actually makes more sense although I still wonder if our Ti doesn't make our Ni more closed. Hmm now I must go think
Hmm. Chalking it up to Ni versus Ne still wouldn't really explain the differences. At least, not in the INFJ. I'm not sure what you mean by 'Ti making Ni' more closed. Ti and Ni do not interact.
But anyway, I was thinking about this, and MBTI-wise, a couple of things were bothering me. Namely, your earlier suggestion that 't
he introverted world has such an integral structure that is so alive and complete (or we'd like to think so) that to "JUST talk" about it is practically an invasion.' This suggest that all introverts would be closed off to discussing ideas and concepts. I do not think this is true. Certain types are perhaps, ah, set in their ways and do not welcome unsolicited critique or outside input when their mind is made up about something. However, where INFJs are concerned, this is definitely not the case.
INFJs use Ni and Fe. Ni is theoretical, pattern-oriented. Fe is about connection, expression, harmony. This brings together a most unique balance and openness to expression and sharing. Indeed INFJs are known to be the 'most extroverted introverts' and this is primarily because of their Fe wing-man. They need outside help to build their inner world. It's not as 'complete' as your comment suggests.
Furthermore, the idea of 'just talking' wouldn't be all that foreign to those with Fe. Consider the types with dominant Fe versus those with inferior Fe to see how this is prioritized in the stack. Types like ENFJ, ESFJ and ISFJ are known for their social niceties and knowing the right thing to say; they are often criticized for being insincere and pithy because they are so quick to say what's needed rather than expressing their own feelings. INFJs are no different.
Dominant and auxiliary Fe makes one more able to adjust to the needs and preferences of the group. For INFJ, their extroverted functions are proof in the pudding: Fe and Se. They're malleable. If the group is talking ideas, INFJ will talk ideas. If the group is just shooting the breeze, the INFJ will shoot the breeze. They do it automatically, without complaint or difficulty as they don't have the same sense of self as say, someone who uses Fi (Fi-types are WAY more particular. That, and Ni gives INFJs an edge in that they can quickly grasp and understand ideas and Fe helps them see the holistic big picture, so they can easily follow along. Once they get more comfortable with their Ti, INFJs simply become better at articulating their own ideas in a group discussion.
Some food for thought.