The core of this debate - similar to debates about abortion, for example - centers on the question, "When does life begin?" Many assert that life begins at conception, when the egg is fertilized. It is often argued that the embryo deserves the same status as any other full grown human. Therefore, destroying it (removing the blastocyst to extract stem cells) is akin to murder. Others, in contrast, have identified different points in gestational development that mark the beginning of life - after the development of certain organs or after a certain time period.
It is legal to conduct stem cell research in the United States, even for the purposes of human cloning. In 2001, President Bush authorized the issuing of federal funds for the research of over 60 existing stem cells lines. The funding was restricted to these cell lines because the issue of life and death was already decided; that is, the stem cell lines at that point were capable of independent and infinite regeneration. In 2009, President Obama reversed the policy and allowed federal funding to be used towards additional stem cell lines.
On August 9, 2001, Bush went further. He announced that federal funding would now be restricted to a limited number of stem cell lines already created by that date—a decision that denied support to many promising avenues of biomedical research in an effort not to "sanction or encourage further destruction of human embryos." Three months later, his administration ordered an official withdrawal of funding guidelines that Clinton had authorized. And with that withdrawal, Bush became the first president to reduce—below what his predecessor had authorized—the amount of human embryonic stem cell research eligible for federal funding. (Reports issued by Bush's own President's Council on Bioethics, which he established by executive order before appointing all of its members, confirm these events in detail.)