Just like emerging through the "trough of sorrow" doesn't seem essential to a strong business yet still seems to do something like what my dad called "building character", I wonder if these ever-present difficulties contribute, somehow, to making people stronger. And even, perhaps, more caring of each other.
"But there's enough troubles already..." yes, yes, I know. But first, it's not a response to the argument. Second, though: what about when those troubles, and then the ones left after that, are eliminated? I've long liked "The Metamorphosis of Prime Intellect" http://www.kuro5hin.org/prime-intellect/ in part because it shows what might be wrong with just such a world.
Would Abraham Lincoln still have been who he was if he didn't have Marfan syndrome? Or what if he was never born because of prenatal screening? If we could eliminate manic depression, would we ever have another Emily Dickinson? Would Van Gogh still have show us the world in new ways if he didn't have epilepsy?
Eugenics has promise. It also holds terror beyond simply how it has been practiced in the past. We're already seeing the dangers of monoculture in agribusiness. Could a similar molecular 'cleanup' of the human genome pose similar dangers?