I think you over use the slogan "there are no guarentees in life." It'd be like letting a 2 year old wander around outside alone because "there are no guarentees in life" as that child could get hit by a car anyway. In a sense it is to claim there is no difference between doing something or doing nothing, because it all is just random and uncontrollable anyway. But its not.
A white man sees a black newborn of his white wife who said it was his. "It is all random and there are no guarentees with genetics." Think he'd accept that as true, that this does not give question if he's the father?
I think it is immoral to give birth to a child and then abandoning the child to the unknown on the premise of "there's no guarentees in life anyway." In fact, if that birth mother committed to the duty to be responsible for her own child - there is a guarentee that someone was being responsible towards that child. Seems rather obvious.
Or I could use your logic of there is no guarentees in life, point to the high percentage of miscarriages, and then just claim "she might have had a miscarriage anyway because there is no guarentees" as a defense of abortion.
Again, though, it comes down to whether a ZEF is a baby or not. You just wrote that is irrelevant? But that is the core of the question. IF a ZEF is a baby the same as a born baby, of course it has an equal right to life. If not, then it doesn't and there is no reason for a woman to birth it unless she decides that is what she wants to do. But that just goes to the total abortion debate issue and the 100,000 back and forth messages about it. I now mostly stay out of those debates as they go nowhere.