A Japanese bioethicist named Masahiro Morioka has done some interesting writing on this (one example). One of his arguments is what he calls "the fundamental sense of security," which is the inherent belief that we are loved and welcomed into the world unconditionally. He questions eugenicist practices to the extent that they demean existing disabled people by saying that, in essence, they shouldn't have been born. But the fundamental sense of security goes beyond that, in that he suggests that this kind of screening makes us all feel like our being welcomed into the world is conditional, and wouldn't have happened if we were too far out of some window of acceptability. In a society that regularly practices this kind of screening, he writes, "people talk about unconditional love; yet they know that they themselves were allowed to be born because they satisfied certain »explicit« conditions imposed by their parents."
I don't know to what extent this is right (and I don't know how firm on it Morioka is for that matter), but I think it's worth thinking about. In particular, the effect on those already-living people with congenital conditions seems much likelier to me. I also think, and this is another thing Morioka touches on in some of his writings, that we have to be careful in boxing ourselves in in terms of defining what "happiness" can and does look like.