(Crossposted from Metamagician and the Hellfire Club.)
It is always worth stressing one more time that the human body and mind were not literally designed by anyone — no super-intelligence was involved, with an arcane purpose of its own. Rather, the body, including the neurological system and everything dependent on it, evolved through a long period of natural selection. Insofar as the process has fine-tuned us for anything, it is not for carrying out a higher being's wishes or for pursuing our own happiness (however we understand it). It is, rather, for reproductive success in the environment in which our ancestors evolved: for being able to survive long enough, in that environment, to find one or more mates, and to pass down our genetic code to the next and succeeding generations.
Wonderful though the body's design may be, and however precisely our organs may perform their work, they are not necessarily ideal for any purpose, and certainly not for our conscious goals and desires in the current environments where we actually find ourselves. As Daniel Dennett puts it: "a benefit to human genetic fitness is not the same thing as a benefit to human happiness or human welfare." Some "design flaws" — seen from the viewpoint of our actual goals and desires — may be quite gross in scale. Thus, Richard Dawkins observes that many human ailments "result from the fact that we now walk upright with a body that was shaped over hundreds of millions of years to walk on all fours."
Walters and Palmer's The Ethics of Human Gene Therapy highlights the difference between people who broadly favour changing human nature, and human capacities, and those who stand in opposition. Walters and Palmer discuss some possible objections to "moral enhancement" in the sense of gene-mediated stimulation of friendliness to others. One objection is that such a choice implies dissatisfaction with, or even disrespect for, our evolved human nature, but they state forthrightly that they just <em>are</em> dissatisfied with, for example, violent aggressive characteristics (they add that the goal would merely be to moderate these, not achieve perfection).
Later, they add two related points: first, that they are motivated by a particular perspective on human nature and the human condition, which involves dissatisfaction with such things as disease, disability, and certain kinds of intellectual and moral failing; second, their positive attitude to genetic enhancement is underpinned by a dynamic view of human nature, according to which we are not fated to accept the historical situation that we've experienced, and are free to enter upon a task of providing a better world for ourselves and future generations, including by planned changes in the characteristics of human beings.
It is not at all obvious why we should be content with what the blind processes of biological evolution have bequeathed us, and why we should not, at least in principle, wish to improve on the result — where the idea of improvement is explicable in terms of efficiency in achieving what we want, as a knife may be improved by sharpening. Looked at in this way, a general attitude of openness to human enhancement — in all its possible senses — may seem more called for than contraindicated.
That is not to deny that there are risks in tampering with something that is, let us remind ourselves, complex and vulnerable. Buchanan et. al., in their superb study, From Chance to Choice, are correct in warning that enhancement may carry greater risks, and less certain benefits, than therapies, may produce unwanted cumulative effects across a society, may lead to collectively self-defeating or unfair outcomes, and may in some cases tempt parents to act on dubious values. All of these points need to be kept in mind, and I will certainly discuss them elsewhere. Nonetheless, the substance of Walters and Palmer's case is the big-picture claim that we do not have to take human nature as we find it. It has no transcendent value, and is, in principle, a legitimate object for suitably cautious attempts at improvement.