Separation of Reality and Fantasy

How often have we read a fictional story and been as much a part of it as if it were an actual, literal part of the world? I remember after we read the Narnia books to my little brother who was somewhere between the ages of 4 and 6, we found him crying in a corner.
"What's the matter, Hughie," our brother Jim said.
"I wish Narnia were real," Hughie said. I shared his sentiment. Still do.
Some studies have shown that the brain activity that occurs when someone is considering some kind of a fictional event is no different than that experienced when considering reality. That means, as far as our brains are concerned, there is no real difference between fantasy and reality.
So when I write a work of fiction, and I do a good job, so it seems realistic to the reader, and the characters are real, and the reader can identify with the protagonist, he/she will experience my story as much as they experience the reality of his/her own life.
That has enormous implications to me as a writer. I have great responsibility to see to it that what I give people, even though it is not strictly historical, is uplifting, beneficial to them. In order to do such, I must seriously consider my own motivations in my writing. Am I writing to get people to pay attention to me, whatever the cost? Am I writing just to entertain myself? Am I writing to benefit mankind, to help people see truth more clearly, make judgments more confidently and competently, find happiness more surely? I hope the latter answer is the true one, but surely the first two are at least possibilities from time to time...