I think it's pretty gruesome, late termination, and I am not convinced it would be my choice either, but each family is different.
One of my friends had an undiagnosed DS baby (no scan) with a terrible heart condition that only lived 24 hours, and I am not sure they would want to go through all that again. Sometimes I think it can be more humane to anticipate things and to find ways to minimise suffering, in a dire situation like that. But nobody should be forced to do anything they feel is wrong.
I imagine numbers of late terminations for DS, cleft palate and so on are miniscule or even non-existent. I expect we are really talking about babies who would never be able to live independently anyway, with much more serious complications and disabilities. However it has become highly politicised as an issue and cases in the media seem very overstated.
The advantage of early diagnosis via amnio etc is that if termination is chosen, it is bound to be less harrowing for mother and less brutal for the child, because the nervous system is not very well developed, if at all.
So I would like to see us working towards increasingly early and accurate diagnosis of serious disability for this reason. For the record, two of my kids have disabilities, btw.