Just because something has the potential to do something great, doesn't mean that anyone who doesn't try to fulfill that potential for that person is stealing something from them. Like if threw a few million dollars at someone, there's a chance that they might go to MIT and cure cancer or some shit. If I refuse to throw the millions of dollars at that stranger, does that mean I stole that money from them and ruined the chance of curing cancer? If a woman refuses to care for a fetus does that mean she's stealing the cure of cancer from the world simply because that fetus had a slight chance of growing up and curing cancer?
It's putting the fetuses life over the woman's.