Saletan points out that arguments being used in support of stem cells are also being deployed with regard to fetuses:

The argument against fetal tissue is that because it's less fundamental and less pliable than embryonic stem cells, it's less useful for research. But in some ways, its advanced development makes it more logical as a source of transplants. As Gardner pointed out, our prospects for engineering completely functional organs from stem cells are "remote." And if stem cells do prove useful in this endeavor, fetuses may still be crucial.