Follow-up: I'm going to attempt a dispassionate discussion about something that, for better or worse, is a big part of who I am.
I'm visually impaired, to the point of being legally blind. Due to some kind of flaw in my development, my optic nerves didn't fully develop (optic nerve hypoplasia), so my visual acuity is far enough below normal that, for example, I can't drive a car, I can only read print up close unless it's huge, and I use a white cane (and often, let's be honest, a sighted guide) to get around in unfamiliar environments.
Should people like me exist? I think if it had been feasible in 1980 to detect the flaw in my development and abort me before my family could develop any emotional attachment to me, it would have been morally acceptable, and perhaps even optimal, to do so. Of course, that wasn't feasible back then, but if our technological development continues, it will be someday, and we, including people like me, will need to consider the moral question rationally, even dispassionately.
Of course, disabled people like me can live full, happy lives, and many do. But it's not guaranteed that we all will. Though my own circumstances are pretty good (in some ways, very fortunate), there are aspects of me, beyond the original impairment, that could objectively be considered suboptimal. There are totally blind people who are much better at navigating unfamiliar environments and living independently than I am. For whatever reasons, attempts to teach me those skills in my childhood and adolescence didn't work very well. To some extent it might even be my own fault. If I hadn't had the natural aptitude and curiosity for programming, and the privileged circumstances to be able to develop that skill (e.g. a family computer when I was 8 years old and ample leisure time for playing with it), I might be far worse off now. Considering how high unemployment is among working-age blind people, I got very lucky. Many of us, even in developed countries, are not so lucky.
In some ways I'm a walking stereotype. I'm musically talented, though I don't make my living from that. I do make my living from being a programmer working on accessibility for people like me. When I read Eric Raymond's "Why I Hate Identity Politics", I wish that my blindness were as incidental to my identity as his cerebral palsy is to his identity. Attempts in my childhood and adolescence to make me well-adjusted and well-rounded, i.e. "normal", weren't very successful. Of course, that could just mean I'm a nerd, but in some contexts, that could be considered an additional handicap.
Even those of us who have mastered all the right skills are often thwarted by gaps in accessibility. The assumption that everyone can see is everywhere. Correcting that assumption, and doing the hard work to make a UI accessible to disabled people, is a never-ending job. That may be job security for a few of us, as long as someone is willing or compelled to pay for it. But in the meantime, people fail to get a job, or even lose a job that they already had, due to an inaccessible application, or even a whole category of such applications. On a smaller scale, people are frequently frustrated while trying to accomplish simple tasks due to gaps in accessibility.
So, to get back to the loaded moral question I raised above, I think it stands to reason that, to modify a popular saying, an ounce of prevention is worth a pound of training and accommodation.
Of course, for those of us that already exist, the latter is still necessary. How much accommodation we should require is another question, though. I'm willing to consider that, beyond a certain point, it's simply unreasonable to expect the whole rest of the world to accommodate a minority like the one that I belong to. I don't know where that cutoff point is, but I lean toward the view that our tools, such as screen readers, should do everything they can to adapt to the world as it is, rather than requiring everyone else to change the way they do things just for us.