Do we want to give our children better opportunities? Forget superficial stuff like blond hair and blue eyes, we're talking about the possibility of having guaranteed super-healthy, super-happy, super-smart children.
But that's eugenics, and it's been rejected as immoral by pretty much everyone. A big part of the problem, I think, is that a custom-engineered child is a lot more expensive to create than a natural random-chance child, and therefore eugenics only produces super-humans for the rich and powerful, who will become even more rich and powerful by breeding themselves into master race that enslaves everyone else.
Eugenics can't upgrade all of humanity directly because natural breeding, being cheaper, is also much more common. So the vast majority of inferior humans will always outnumber the eugenics-produced super-humans. That's where the enslavement comes in; the super-humans will have to use their inherited wealth and power to make sure they retain control because they can't out-breed everyone else.
The other possibility, and the only way the super-humans can replace the normals, is to kill off all of the normals either directly or by making them infertile. That's even worse than enslavement.
No matter how you look at it, eugenics has a bad outcome if it's not available to everyone at the same time. And if it was available to everyone, we wouldn't call it eugenics. We'd call it 'medicine', 'vaccination', 'pre- and post-natal care', and 'preventative care'.
Selective sexual reproduction and genetic engineering are actually markedly different. Genetic engineering involves precise splicing, insertion, or rearrangement of an organism's genome (or subset of genes). Selective sexual reproduction is a directed random rearrangement of genetic material over successive generations based (on often poorly understood) "meta-characteristics" or traits.
The critical distinction is that genetic engineering is the deliberate editing of exact genetic information, whereas selective sexual reproduction is a gradual, iterated, locally-random mixing of genetic information with imprecise results.
Furthermore, genetic engineering enables genetic mixing that aren't possible with selective sexual reproduction. For example, the insertion of genetic information into E.coli in order to produce human insulin for diabetics. Or, the modification of a particular cyanobacteria to secrete petroleum after photosynthesis.
http://pubs.rsc.org/en/content/articlelanding/2014/gc/c3gc42...
>> ...eliminating allergies, Alzheimer's, and cancer...
> That's all been doable for a long time, using controlled breeding...
This is incorrect. You may be surprised to learn that those deeply complicated, diverse families of afflictions would not be effectively treated via 'controlled breeding'.
A simple, naive disproof of the assertion that cancer can be eliminated in domesticated or selectively selectively bred animals (via artificial selection): pigs, huskies, and laboratory mice all get cancer at rates that are more or less congruent with wild boar, wolves, and rats.