There is a very dark side to genetic screening and engineering. In the case of overcoming sterility, it is far more understandable, but to micromanage the outcome of conception itself, or to decide who and who will not be born based on genetic criteria, raises a whole lot of red flags!
Science is only beginning to understand the role of so-called "junk DNA" in assuring the long-term survival of our species. Even the role of viruses is largely a mystery - we've only begun to appreciate the tremendous role viruses play in disseminating important genetic information upon which the survival of many species (including our own) is hinged. Things are not always what they seem - there are no "accidents" in nature, and even the most seemingly insignificant, or weakest link (human or otherwise) has a significant part to play in every biological system. The same is true on a cultural scale. (For greater insight into this subject, please read "Survival of the Sickest by Dr. Sharon Moalem.)
If we were to screen out all but the "desirable" traits in future offspring, we could end up cheating a great many "imperfect" children of the gift of life itself.
Do we want only pretty, intelligent and/or athletically capable children? Are we breeding race horses or embarking on a lifetime of becoming loving, effective parents? Ensuring that our offspring would be free of genetic diseases certainly doesn't assure that they will live long, fruitful lives - or that they will win marathons, overcome many of life's hurdles or go on to be loving, effective parents themselves.
Some of the sweetest, most endearing individuals have come into this world with genetic defects. Down Syndrome, high cancer risks, mental retardation and extreme physical abnormalities have not stopped many individuals from both receiving and giving a wealth of love during their lifetimes.
Albert Einstein was imperfect; so was Thomas Edison (a poster child for ADHD), and Walt Disney was considered "learning disabled" as a child. Was Mother Theresa considered a flawless physical specimen - oh, and how about Helen Keller? Who's to assume what genes will produce the most indispensable future additions to the human race? It does seem like genetic screening/engineering wholly misses the point.
Nature has a built-in mechanism for increasing the likelihood of successful reproduction within the human species. The "chemistry" between individuals during the courtship phase itself tells a lot. The makings of initial attraction between potential parents are not altogether random occurrences. Below the threshold of human consciousness, we select our mates based on many biological criteria, including how well their immune systems will mesh with our own.
It's not just about "classic beauty" and other aesthetics, high IQ or even character traits that set our procreative hormones in motion ... it is also a lot of behind-the-scenes biological criteria that we are only beginning to understand, and it seems to have very little to do with flawless genes. The human race has managed to thrive on our planet for millennia, often against insurmountable odds - all that without genetic engineering. Oddly enough, it is often the misfits, the least "perfect" among us that manage to drive humanity forward and touch the hearts of many.
Successfully populating the planet with the most advantageous mix of human specimens is not the business of genetic science. It never was about perfection - it was about harmony, diversity, and most of all, learning to love and be loved.
It is one thing to select a mate based on attraction to that person's chemistry, virility, intelligence, physical beauty - and quite another to micromanage the genetic makeup of our offspring.
To decide based on genetics, whether or not a child would be worthy of life is pure folly, and expensive folly at that. Hitler tried it - even Plato envisioned something similar in his "Republic" which Hitler - and Mussolini - were influenced by. There was no room for genetic imperfection in the "Republic." History has proved to us that such a social experiment is bound to fail - tragically.
Selective breeding whether enacted in a laboratory or dictated from a political platform paves the way for a whole lot of unspeakable horror - history has already proved it so.
Who, but the Creator has the authority to decide who should or shouldn't get to be conceived and born? Certainly not mere humans, with mere human understanding. There is a much, much bigger picture - a gestalt, if you will. Science can barely touch it.