- I don't understand how the ability to distinguish between intrinsic and extrinsic finiteness would take us into religion.
It doesn't. Your proposal about intrinsic vs extrinsic "finiteness" is wrong, not religion. Your concept of infinite "selves" is what takes us into religion. So does your implication that someone or something must chose from this infinity to make certain that twins get similar selves.
The SM, as you call it, does not allow for infinite potential selves; in this model the "self" arises directly from the physical brain and is constrained to a finite number of potential selves based on the physical structure of the brain (which depends on its genetics, random chance, and on its experiences from day 0). This number may be very large, but is not infinity, as much as you would like to divide 1/infinity to make your equation fit your pre-existing goals.
In fact, the SM implies that every human brain will
inevitably form a "self," a self-perspective. That "self" may not be Jabba per se; it may have been your sibling, or me, or one of 7 billion others. But it will inevitably form a "self" of some form (probability "essentially" =1) that is based on the physical brain.
As previously explained multiple times: in advance (posterior probability), that "self" had a low chance or being a Jabba per se, but it certainly it had to be someone. You happened to be Jabba. I happened to be me. I am holding a particular number in my hand from a large set of lottery tickets, although that particular number was highly improbable for me to select before I selected it. What is hard to see about this?