Yes I agree, SC.
As a general principle, I am in favor of letting the mother choose to abort or not to abort. But the sooner in the pregnancy the better, as a rule of thumb. I find the concept of late-term abortion disturbing at best, and in general I hope to see better technology soon that will increasingly enable abortions that don't cause suffering to the child.
I've noticed that all questions about abortion come without absolutes. There is no way to precisely define "too late in the pregnancy," for example. There is no way to precisely define "suffering too severe for the child." And I can't fathom where one would draw the line between "able enough" and "too disabled."
If she knew how crippled he'd be, and if we assume she had a choice, did Stephen Hawking's mother choose well in carrying her son to term? Well, anyone would say yes, of course, obviously, but what if she'd had no idea what kind of I.Q. he'd have, and what if she'd had reason to believe he'd be mentally handicapped? Then carrying him to term would be a leap of faith, and the high intelligence he proved to have would be a bonus in light of the prenatal expectations.
With that case in mind, how does one decide what quality of life is too low for a child to have to face? From what little I know of Stephen Hawking, it seems to me that he is glad he was born and wouldn't have it any other way. And additionally, a mentally-handicapped child isn't doomed to an unhappy life either, as AlwaysGrowing pointed out.
We keep pets that (we think) have well under average human intelligence, and don't consider their "handicaps" (their inability to speak English for example) to be reason they can't have a joyful life with us -- bringing us joy, and receiving joy from us. In fact lots of people keep houseplants which can't even move or care for themselves beyond processing sunlight and minerals -- just because we like the life that living things bring to our home.
In spite of all that, I imagine that if I was a woman and pregnant with a child who I knew would almost certainly be born with so many internal/external deformations as to make it very challenging for that child to stay alive, I would probably abort. If I knew my child would be somewhere in the ballpark of that level of internal/external deformations, I'd be strongly tempted to abort -- but I don't know how anyone can make such a weighty decision based on some one-size-fits-all standard. I think you have to be in the situation, and even use some intuition in deciding. Very difficult.
A really challenging, troubling story about these kinds of decisions can be found in the following article:
http://blog.sfgate.com/sfmoms/2013/03/05/surrogate-mom-refuses-to-abort-fetus-with-birth-defects/
If we had a special time machine that allowed us to visit an alternate future in which a "badly" (What constitutes "badly?") disabled child had been carried to term and lived at least five or ten years, we could ask that child if xe was glad to have been born in spite if hir disabilities. How many kids, honestly, even badly-disabled kids, would say they wish they'd never been born? Well we all say that at certain really awful points in our lives -- but how many of us really, consistently feel that way? Not many, I bet.
Shoot, even if you knew your child was merely going to be gay, you could rationalize an abortion by saying, "This child will go through life as a social pariah. It would be better to spare hir the angst, anguish, and lonesomeness xe'd have to endure for hir orientation. If this was more of a gay-accepting world then I'd carry hir to term." Ah, if only we had that special time machine and could interview the child-if-xe'd-been-born. Then we could get hir thoughts, feelings, and state of consent. But most of us obviously agree that you'd carry a "gay child" to term -- a life of social persecution notwithstanding.
Essentially, an abortion -- and indeed, the choice to carry to term as well -- is an attempt to predict the future. It is a prediction that every pregnant woman has to make, if she has any choice at all about aborting. Substantial risk of life to mother and/or child perhaps makes the choice more obvious. And then there's pregnancy by rape which is rather off-topic here but I mention it just to further illustrate how complicated the whole issue of abortion is.
They say women tend to be better at knowing their own hearts than men. I don't know if that's true, but it'd certainly be an appropriate advantage in making tough decisions about one's unborn child. You can't carve things down to one-size-fits-all rules, so you have to guess with the help of your heart! Is there any other way? None that I can see.