Ethics down to the disulfide bond

Writing about new, less ethically objectionable stem cell production techniques, William Saletan predicts that "The stem-cell war will be dead. So will the biological sanctity of human life." Huh? If we end up going through a bunch of extra technical hoops to make sure we don't kill an actual embryo, we will have established a de facto ethical consensus that human organisms, even in their earliest stages of development, are something we may not kill like livestock. To me, that sounds like affirming the biological sanctity of human life. (Or perhaps I misunderstand what Saletan means by "biological sanctity.")

Some people think that if the difference between some human organisms (zygotes) and mere human tissue (products of ANT) is just a matter of a few chemicals, then the moral value of these human organisms sinks to the moral value of human tissue. But why can't a great moral difference be a matter of a few chemicals? The vaccine for yellow fever is live but attentuated versions of the very viruses which cause the disease. Yet, the moral difference between giving someone the vaccine and giving him the virus is very great indeed. By itself, this argument by analogy doesn't prove that a few genes and/or proteins constitute a line between manslaughter and mere cell slaughter, but I do believe such moral lines exist, and that we will discover many of them as biology advances.

The greater bioethical quandaries lie where there are continua instead of dichotomies. For example, after we have the technology to create (for lack of a better term) subhumans (possibilities include human-animal chimeras), I doubt a clear moral line between human and subhuman ever will be found. Similarly, if a man could radically alter his brain, then after how much alteration would he become a different person? Does it matter if the alteration is abrupt or gradual?