I'm glad to know that someone is taking Our Posthuman Future seriously enough to want to trash it, and I guess it's an honor to be the object of Extropian scorn. I didn't know that they existed in Sweden, though—I thought this sort of thing was more home-grown American. In Europe I found myself mostly criticized more for being too permissive on biotech issues.
I think that the closest parallel to a ban on reproductive cloning would be the existing ban on incest. Incest, as you know from your work on evolutionary psychology, is actually a fairly rare thing that people by and large are not itching to do, and yet all societies have passed laws restricting sexual and reproductive rights in this regard. If you asked people why they support an incest ban, they would respond with some mixture of safety/health and moral concerns (though maybe attitudes are changing even on this …). It is possible to construct a sympathetic incest scenario, similar to your Chloe case. Perhaps a brother-sister or father-daughter pair had lived apart, but met, fell in love, and suddenly discovered that they were the most perfect people for one another. We could test for double-recessive genes to make sure they didn't pass on birth defects—so why should we keep them apart just because they are genetically related?
The fact that you can describe a sympathetic scenario is no more a justification for permitting incest than it is for cloning. (Indeed, you could find sympathetic scenarios for doing many things that are banned today, like murder, robbery, fraud, and the like.) Reproductive cloning, like incest, would be a fairly minor issue either way: There aren't likely to be many Chloes out there, just as there won't be a lot of teen-age bombshell clones tempting their fathers. The reason for an outright ban is, as in the case of incest laws, a mixture of safety/health and ethical reasons.
Since the safety concerns are well-understood (i.e., the large number of deformed fetuses produced in cloning experiments), let's focus on the ethical issues. Human reproductive cloning will be the first instance in which parents will have specified the genetic makeup of their child in advance of the child's birth. It will involve deliberate human manufacture and thus will set an important symbolic precedent that will legitimate more powerful and ethically questionable germline genetic interventions in the future. We don't want to get used to the idea of human genetic engineering, even if the procedure becomes safe, because this opens the door to new types of social engineering that will prove no less costly than those that were attempted in the past century.
A ban is important precisely because it lays down a marker that there are certain moral limits that the society will not cross and that we will not in fact do everything that technology allows us to do. Americans—perhaps due to their experience with information technology—often believe that technological advance is unstoppable and unregulable.
But this is clearly not true: We regulate, with greater or lesser success, nuclear weapons, drugs (both legal and prescription), toxic materials, dangerous germs, environmentally damaging emissions, and a host of other byproducts of our technological society. In an area that hits closer to home, we seriously slow down the pace of biomedical research to protect human subjects. Last summer the federal government shut down all of the clinical trials taking place at my own university, Johns Hopkins, because of the death of a volunteer in a research experiment. If drug companies or researchers had the freedom to take advantage of poorly educated or desperate people in clinical trials for drugs, we could have them on the shelves much faster than we do today.
The fact that no rules are ever fully obeyed is not a reason for not having them in the first place. Which brings me to your last point about our inability to police the broader international community. I don't think this makes the slightest difference in regard to a reproductive cloning ban. The fact that rich people could go elsewhere to get themselves cloned doesn't mean we need to follow suit. After all, a rich person desperate for a new liver or heart could go to China today to buy one, and I'm sure some do. This doesn't mean that we should race the Chinese to the bottom by following their policy of involuntarily harvesting the organs of recently executed prisoners.
So, Bob, I'm one of those conservatives that believes that values trump the market in certain cases. And you've got to plead your case using advocates other than the Raelians or Extropians—the Supreme Court has already ruled that religious freedom under the First Amendment doesn't justify any religious practice, such as bigamy or ritual sacrifice, that a sect believes itself entitled to perform.