Yes, absolutely. I don't think there's anything wrong with parents hoping that their child won't be disabled, either. However, as many experiences have shown, parents kind of have to actually meet their child first to be able to love the child, and God knows there are plenty of 'non-disabled' children for whom the relationship to their parents is less than ideal.
Apart from that, one of the main reasons for the stigma surrounding learning disabilities in particular, I think, is a deeply-ingrained idea that somehow it's a bad thing if someone has to be cared for. Sure, we would all wish that everybody could be fully independent, but if someone has to be cared for, that shows the importance of care.
You sometimes get the impression that it's almost as if some people don't want to be confronted with that idea, much as many don't want to be confronted with the reality of homelessness, for instance, or the 'work' (which is obviously not voluntary) homeless people often do in reminding people that these injustices exist.
Needless to say, people with learning disabilities are very different, but there is something about someone having to be cared for that brings people together around them, and difficult though that sometimes is, it is a good thing and improves our idea of what it means to be human. It's for that reason alone that we should value the existence of learning disabilities, and the people who have them, while all the other reasons obviously apply.