What is the primary concern regarding the ethical use of embryonic stem cells?

The primary concern regarding the ethical use of embryonic stem cells centers on their source, which is embryos. The use of embryonic stem cells typically involves the destruction of embryos, raising significant ethical questions about the value of human life at its earliest stages. This concern embodies a range of philosophical and moral issues, such as debates about when life begins and the rights of embryos as potential human beings.

In contrast to this central ethical issue, while unlimited self-renewal is a characteristic of stem cells that has potential implications for research and therapy, it is not inherently an ethical concern. The method of extraction can involve ethical considerations but is primarily secondary to the implications of using embryos themselves. Lastly, the development of unwanted tissues, while a technical concern in therapy and research, does not hold the same weight in ethical discussions as the implications surrounding the destruction of embryos.