McQuilkin and Copan argue that while adult stem cell research is morally acceptable, embryonic stem cell research is not.

Why is embryonic stem cell research immoral?

Obtaining embryonic stem cells involves killing unborn humans

Explanation:

McQuilkin and Copan describes stem cell as cells that have the ability to divide different cell types and are source for various tissues in the body. This recreation ability have led to the development of Embryonic stem cell where these stem cells are harvested from unused embryos. McQuilkin and Copan argued that it involves killing unborn humans and it is therefore morally wrong. They however argued that adult stem cell research is morally permissible