Even some on the whole pro-life people think that an abortion because of fetal disability can be justified. But such an abortion suffers from a particular vice. I am not saying it is worse than other kinds of abortion, since these others may have their particular vices, too, but it is morally bad in a uniquely problematic way.
The problem is that in such an abortion, a child is killed by one or both parents for not measuring up to a standard through no fault of her own. A way of seeing what is problematic with such an abortion is to reflect on the disposition of a couple who would have had such an abortion if their child had turned out to have a disability of a certain magnitude, but because their child either did not have a disability, or did not have a disability of that magnitude, they did not abort. Such a couple, unless they have changed their attitude (as hopefully they have), do not seem to love their child unconditionally. For they had a standard such that had their child not measured up to it, they would have had the child killed.
What I said above assumes that the fetus is the numerically same individual as the later child. I have argued for this thesis elsewhere, but to those who are not convinced by that thesis, what I said above will not be convincing. However, if one is generally pro-life, one likely accepts this thesis, and hence one should accept that to have a disposition to abort should there be a sufficiently serious disability--whether or not one acts on that disposition--is morally deeply problematic, both in regard to a child who is aborted and in regard to a child who is not.
I also think the above considerations have some weight even if one drops the assumption that the fetus is the numerically same individual as the later child, but instead assumes--as seems very plausible--that the fetus is sufficient to determine the identity of the later child. (I.e., that it is false that in one world, fetus A grows into child B, while in another world, the same fetus A grows into a numerically distinct child B.) For in such a case, we can reasonably say that to judge whether or not to abort on the basis of what the child is going to be like is indeed to pass judgment on that later child, since there is a definite possible future child whose numerical identity is already determined, and to do that is to endanger unconditional love for that child should that child live. (This is different from a case of contraception, where typically there is no definite child determined at the time the contraception is used; it may be that some argument like this can be adapted into an argument against contraception, but this argument as it stands does not of itself seem to prohibit contraception.)
This argument is a special case of one that I have made elsewhere. But I think the case of disability is a particularly clear case of the more general problem. To give credit where credit is due, both arguments are inspired by insightful remarks Wilfried Ver Eecke once made in a conversation with me about unconditionality of love, psychoanalysis and abortion.