If we go too far down the road of choosing the genetic traits of children, my worry is that parenting will be less a kind of school for humility than it should be, and we will become too accustomed to regarding children as instruments of our ambition and of our desires.
The other effect that I worry about is the effect on the parent, that the moral teaching of humility and of the limits to our control that parenthood teaches- - that that will be lost and that we will begin to think of children more as consumer goods than as gifts that we can't fully control and for which we aren't fully responsible.
Parenthood is a school for humility. We can't choose the precise traits of our children, and that is morally important. It teaches us what William May, a theologian whom I greatly admire, calls "an openness to the unbidden."