The overshadowing argument against this, is the "slippery slope" argument. Today you can reliably screen for Downs, and most of the developed world do. Tomorrow it might be for Huntingtons (btw, we're making progress on testing a fetus for all kinds of genetic markers with a simple blood sample from the mother). But when will we stop? Predisposed for depression? Anger issues? Dwarfism?

I agree that for simple things such as Downs and Huntingtons it's fine. I'd prefer to know as a parent, but we need to have a deep and reflective discussion about the ethics and agree on the guiding principle for the future.