One of the fields in philosophy that I spend a great deal of time studying is population and procreative ethics, simply because there are so many conflicts and contradictions between our intuitions. Sometimes it can actually be somewhat vexing how unrefined our intuitions are in regards to this sort of thing. They are literally "issues at the edge of life".

Say a person has cerebral palsy. They have difficulty moving and living "normally", although with modern medicine and technology they may have a shot at living "normally".

Anyway, this person was once a child and before that, simply an idea or even an accident. Had the parents known this person would have cerebral palsy, might they have abstained from sex or aborted the fetus?

The non-identity issue comes into play when we realize that if the parents did prevent this person from coming into existence, and either waited to have another child or abstained entirely (the latter being preferable from my perspective), they wouldn't have actually benefited anyone. The person exists either with cerebral palsy, or they don't. There are no conditions in which they are free from their disability.

Now a related issue, then, is how we see disabilities in general. Why would we feel compelled to abort the fetus of a person with cerebral palsy? Might we be concerned about their well-being, their quality of life? Are we not, by considering abortion, already considering that a life with cerebral palsy is not worth living?

But say the person comes into existence and indeed has cerebral palsy. Nobody would really tell them that they thought their life was not worth living, even if they secretly believe this to be so. Curiously, parents of children with all-things-considered deprecating disabilities still love their children greatly - but if they knew their children would have such disabilities beforehand, would they still have them?

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Thus we come to an instance of tension between intuitions - on one hand, we (secretly?) believe disabilities are all-things-considered undesirable and not something we personally would want to have, but neither do we want to insult those who do have disabilities by saying so. And of course we don't want to go to the extreme and start a eugenics program...but look ahead a few decades from now and we might be having designer test-tube babies. Is this not eugenics?

Another tension has to do with starting a life of disability and continuing a life of disability. If a life of disability is, all things considered, not worth starting, or at least not worth starting in comparison to "better" lives, how is it that a life of disability is worth continuing? Is there trulya difference between starting and continuing, from a basic level?

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My view on things is that what we see as value has its most robust form when articulated in terms of what actually exists. The non-identity problem is only an issue when we demand to use value comparatives, like better-than or worse-than, instead of more concrete value determinators, like worthiness or shittiness.

This has further implications. I believe such a immanent value axiology inherently motivates people to live fuller, appreciative, and realistic lives. You either exist, or you don't. It brings a whole new meaning to the Nietzschean amor fati, and also brings along the disturbing implication that some (or perhaps all?) lives are essentially and inherently not worth living.

A consequence of this would be that (assuming birth is not morally problematic itself...), abstaining from having a child with a disability simply because they have a disability is a bad intuition, unless the disability is widely recognized to be incredibly detrimental to the person with it. You're not technically doing anyone any favors by not having children, but you are making sure nobody has any problems, and unless the disability by itself (or anything else for that matter) is enough to make a life not worth living, it technically doesn't make sense to contemplate not having the child for its own sake.

I say technically because I realize how tiresomely hair-splitting this may seem to some, and how it seems to be simply a misunderstanding of language or something. Which I don't think it is.