I wouldn't call that pessimistic. Fine-tuning traits like intelligence, strength, height, etc are in my opinion the thing that's going to lead to designer babies. The longer we stay away from that, the better.

I can certainly see the case for fixing genetic defects, though as the sickly cell/malaria example shows, that's not always clear cut either. And even if you just fight genetic defects, if it's only available to the rich, it's going to create a genetic class system where the rich literally have better genes than the poor. I shudder to think what that might do to a society.