Eugene Volokh takes the libertarian position that society will not be adversely affected by rich people having the first access to genetic modifications for their children. In his case, the libertarian argument is "less government". Many years ago, I took a nearly-opposite, libertarian position, that no one should be allowed to manipulate an individual's genetic identity, at least as far as personality and intelligence are concerned. Volokh appears to completely miss the possibility that genetic improvements may have a down side for freedom. This might be an interesting contrast in whether the libertarian position is "less government" or "more individual rights."
But what about the reasonable libertarian position? I now find it harder to say that gifts like tremendous intellectual ability and freedom from mental illness should be rejected because of abstract beliefs in the sanctity of randomness when our chromosone set is conceived. On the other hand, I think there's no defined line between eliminating genetic mental illness and creating dutiful, obedient children (and citizens?). And I can't believe that even purely intellectual improvements won't also have profound effects on personality.
What decides the issue for me is that I don't have to decide it. People ARE going to genetically modify their children, no matter what the law says. If genetically-modified genius children are outlawed, only outlaws will have genetically-modified genius children, and that situation won't last very long. So embrace the brave new world, because it's coming, and a lot of it's good. Our genius children will tell us if we've screwed up.
Some additional notes: someone else caught the personal autonomy issue in the Volokh comments. Also, Volokh mentions Gattaca, but I think Soldier is another relevant movie to reference. Finally, to make this somewhat more topical, I don't really have a problem with embryonic gender selection - it will ultimately make girls more desirable in the Third World and less discriminated against.
UPDATE: Reason magazine has an article on this subject. Note the virtually unstated assumption that improving part of one's intellect will have no consequences on other parts of intellect or personality.