From an excellent article by Robert P. George and Patrick Lee titled Acorns and Embryos:
[Via Southern Appeal]
Part of the problem we face is the way the issue has been framed by the editors of the New England Journal of Medicine and many others who have waded into the debate. Absent the appropriate framing of the issue, there is little likelihood of generating an illuminating public discussion.
If we were to contemplate killing mentally retarded infants to obtain transplantable organs, no one would characterize the resulting controversy as a debate “about organ transplantation.” The dispute would properly be characterized as a debate about the ethics of killing retarded children to harvest their vital organs. The issue could not be resolved by considering how many gravely ill non-retarded people could be saved by extracting a heart, two kidneys, and a liver from each retarded child. The threshold question would be whether it is unjust to relegate a certain class of human beings—the retarded—to the status of objects that can be killed and dissected to benefit others.
By the same token, we should not be speaking in terms of a debate “about embryonic stem cell research.” No one would object to the use of embryonic stem cells in biomedical research or therapy if they could be harvested without killing or harming the embryos from whom they were obtained. Nor would anyone object to using such cells if they could be obtained from embryos lost in spontaneous abortions. The point of controversy is the ethics of deliberately destroying human embryos for the purpose of harvesting their stem cells. The threshold question is whether it is unjust to kill members of a certain class of human beings—those in the embryonic stage of development—to benefit others.
The article then goes on to answer the question "But are human embryos human beings?" This article was written in response to an article written in the New England Journal of Medicine which advocated various reason why it is morally licit to use human embryos for research. They answer all of the arguments used so as to totally destroy the and to show as absurd the analogies used. This article is well worth reading in full.