Sorry, but I still don't think you've answered my big question: What would be wrong with parents choosing to genetically engineer a child less prone to hatred and violence than the typical human being?
You note that impulses like hatred evolved in tandem with our instincts for sociability. True: During the Stone Age, hatred and retribution were nature's way of helping us defend our interests in the complex non-zero-sum games that constitute social life. But that was then. Today we're protected by police and judges, so violent rage isn't especially useful equipment.
Moreover, the fact that "good" and "bad" traits—e.g., sociability and hatred—are intertwined in their evolutionary history doesn't mean they're hopelessly entangled physiologically, as you suggest. Drugs like Ecstasy make it pretty clear that you can mute one without muting the other or amplify one without amplifying the other.
To be sure, tinkering with human nature will in general be messy, with unintended consequences, as I've already conceded. (Ecstasy apparently does brain damage in the long run.) And if genetic tinkering is so messy that it unavoidably creates miserable mutants, that will be grounds for banning it even by my lights. But you believe this tinkering would be wrong even if it weren't messy. It's the philosophical foundation for this belief that I'm trying—without complete success so far—to get you to crystallize.
Speaking of philosophical foundations, I think you're a little unfair to mine: utilitarianism. You say that if I see virtue in a fireman or Mother Teresa, while taking a dim view of an unscrupulous but happy CEO, I must not be a utilitarian. Au contraire! I attribute virtue to Mother Teresa and the fireman precisely because they are effective utilitarians. By making sacrifices that allow many others to live, they're increasing the total amount of well-being in the world. I scorn the crooked CEO because his well-being comes at the expense of others' well-being.
Similarly, you seem to believe that to condemn slavery one must go beyond utilitarianism. I beg to differ. Slavery leads to unhappiness; I rest my case. Of course, you might be able to show me one or two happy slaves. But I contend that a society in which ownership of humans is permitted will on balance be less happy (and more vulnerable to various happiness-reducing social and political corruptions) than a society in which slavery is banned.
Note that I just rejected slavery without embracing your moral language of human "dignity." But note also that I could embrace such language and still keep my utilitarian credentials. If giving such concepts as human dignity and human rights a privileged place in moral discourse increases overall societal welfare, as I believe it can, then even a utilitarian can take these concepts seriously—but as derivative values, not as self-evident, foundational ones. In your book you don't grant utilitarianism this much flexibility, but then again its critics seldom do. (They usually describe "act-based" utilitarianism, rather than the more powerful "rule-based" utilitarianism. But don't get me started on that.)
As for your asking me about my grounds for defining a "better human being"—and whether it would be "better" for my wife to choose to have a gay child or a straight child: Well, broadly, my grounds are utilitarian: Which child would be happier and more conducive to the happiness of others? But like all moral philosophies, utilitarianism doesn't spit out an easy, automatic answer for every specific case. The murkiness of these specific cases is one reason I believe it may be better to leave them in the hands of individual husbands and wives (and individual gay men and women who want to use clonal technology, if that's ever safe, or in vitro fertilization), than to let the government lay down the law. And, as I see it, for the government to ban these technologies is for the government, in effect, to intervene in lots of individual moral decisions.
OK, so there's the moral basis for my position, as best I can articulate it briefly. Now I'd like to hear more about the moral basis for the stringent restraints on biotechnology that you'd like to see. Meanwhile, let me lay out some more doubts about their feasibility.
In Our Posthuman Future, you powerfully demonstrate the blurriness of the line between correcting someone's behavioral pathologies and augmenting their behavioral arsenal. Attention deficit disorder is a pretty vague thing, and Ritalin is prescribed to people ranging from the seriously afflicted to the slightly distracted. It seems to me that this sort of continuum is what will make it hard to draw the legal lines you'd like to draw.
For example, presumably the government won't prevent a woman from using germ-line interventions to avoid having a severely retarded child. (And surely the island-state of Extropia won't!) And, once that precedent is set, what about mildly retarded children? What about children with a slight "learning disability"? Pretty vague term, "learning disability." And I suspect that, as reproductive technology leads to fewer and fewer children being born with traditional learning disabilities, new "disabilities" will be recognized, since "disability" is defined relative to the norm. So even if we confine germ-line engineering to the prevention of "pathologies," we'll be embarking on a path of limitless augmentation. It's hard to imagine humanity not stepping onto this path—because the first steps will, plausibly, strike most people as good.
I want to stress that I share some of your qualms about where the path will lead in the longest run. We've already talked about the possibility of society becoming sharply stratified genetically. (I got an e-mail yesterday informing me that this scenario is explored in Remaking Eden by Lee Silver, whom you cite and who spoke at the aforementioned Sweden conference.) As a partial antidote to that scenario, I hope society will establish the principle that whatever germ-line interventions are permitted (a growing list, I predict) should be available to all parents who want them, even if that means the government pays for them. It's creepy to have the government subsidize these things, but not as creepy as having Manhattan and Trenton populated by two separate species.
It's been fun arguing with you. I wish we had more time, so I could convert you to utilitarianism and get you to repudiate your Aristotelian past. Instead, I'll just watch helplessly as you get the last word.
Finally, let me express the hope that this Ted Williams cloning story has gotten you and your book some air time. If not, America's TV and radio bookers need to be genetically augmented, something I know you'd be in favor of.