Serious reply (in that I am really interested in this question).
According to Fowler's Stages of Faith, my [instantaneous] answer would be that...
1) Flat Earth "believers" may somehow be still stuck in Fowler's Stage One: Intuitive-Projective faith ("...characterized by the psyche's unprotected exposure to the Unconscious. Imagination runs wild in this stage, uninhibited by logic"), which may be mixed with...
2) Synthethic-Conventional faith (Stage Three), depending on what social and family influences might be in play.
[This would necessitate skipping Fowler's Stage Two: Mythic-Literal Faith, but my take is that genuinely believing Flat-Earth believers have to have some serious empty spaces SOMEWHERE in their psyches.]
TBM's, on the other hand, are probably skewed very heavily as Stage Three: "The majority of the population finds its permanent home in this stage. Usually arising in adolescence, this stage demands a complex pattern of socialization and integration, and faith is an inseparable factor in the ordering of one's world. It is a stage characterized by conformity, where one finds one's identity by aligning oneself with a certain perspective, and lives directly through this perception with little opportunity to reflect on it critically. ... Authority derives from the top down, and is invested with power by majority opinion."
[The quotations above are taken from: STAGES OF FAITH: The Psychology of Human Development and the Quest for Meaning, by James W. Fowler.]
In other words, and assuming we are talking about fully-grown adults, TBM's would likely have risen to, and are stable in, Fowler's Stage Three...
...while Flat Earth "believers" (also assuming they are fully-grown adults) are stuck in Stage One (which Fowler says "usually occurs between the ages of three and seven").
Edited 1 time(s). Last edit at 01/08/2018 11:04PM by Tevai.