We are unable to disprove the existence of anything that doesn't actually exist. Yet, we are not agnostic about all of them. In fact, we comfortably live our lives as if these things are not real. Even in some of the cases where we do believe, we still live our lives without constantly peering over our shoulders.
The "agnostic" part of PIMA is doing some incredibly heavy lifting, and it's a smokescreen. What the A really stands for is "afraid." Afraid of losing family and friends to shunning. Afraid of losing the only social support that you were allowed to build. Afraid of losing stature in the small, tight-knit community you can't seem to escape. Let's call it what it is: Physically In, Mentally Afraid. Agnosticism has nothing to do with it.