Part of what is cool about having kids is finding out what they look like/personalities/ interests are, etc...and just seeing how they are, as they are. It seems very creepy for the parents to be able to decide thkngs like that.
With my last child when we did the blood test at the beginning of my pregnancy, it said the baby had a very high chance of having downs syndrome. Being in that position, if there was a way too correct that, I think it would be hard to turn down if it could be done safely.