Still not seeing the difference. Remove the machines and the brain dead person dies. Remove the mother and the fetus dies. It obviously is having trouble functioning without the mother just the same as the brain dead person cannot function without machines.
Maybe we have differing ideas about the functions of life? To me it appears as though a fetus without a brain has the same functions as an adult who is brain dead.
It's not about dying, and no that's really not true.
I was assuming basic biological knowledge when I made that post (I believe that qualifies as common knowledge).
A cell-based structure, use of energy, use of nutrition, production of waste materials from both, response to simulation, self-regulation, reproduction, ability to pass traits to off-string, and a hereditary history.
Source
So, the fact that they can't survive on their own is irrelevant, quite a few parasitic/symbiotic organisms cannot survive without what they have a relationship with, it's the ability to perform these functions of life that counts.
A fetus can (after a certain point in development, I'm not sure of the exact biological cut-off), a brain-dead person on a machine cannot.