Hi, I am a med student and my wife is a biology researcher so I will try to give my thoughts not only from the ethical base but also from a practical scientific point of view.
Regarding ethical points:

1. The population explosion threat is something I am really worried about, it started after I read the book Inferno by Dan Brown, a most read book by the way. Eventually I decided that in my opinion - humanity should advance ideas to deal with this problem, like settling on Mars and so on, in parallel to the advances that bring upon us the population explosion. there is every reason to believe that science can find solution to a problem stems in a technological advances with another technological advance.
2. Regarding the decision making by parents and the alternative view of people with disabilities as, in some cases, happier and whole in their own way - I do accept the view that there are many ways, almost unlimited ways, to look at the world - this is the core of the postmodern era, but - in the end, in order to live a normal life, every individual has to decide what is the point of view he agrees with the most, and in cases when there is no way to back off - one has to act according to his beliefs even when they affect other person, his son in our case - with the belief and hope that he does the right thing for the other person in the most acceptable way.

Now - practically - my and my wife's professors do not care much about ethical observations - the academic world is like a race - every person in this world tries to get to the next finding faster than the plethora of other scientists working on the same thing, and they will do almost whatever they can to achieve that. Therefore those questions you rise are extremely important, but it should be pressed that the government, with the assistance of ethics professionals and philosophers, should contemplate this issues - draw guidelines and then force them on the scientific world.