That’s the subject of a controversial new paper in the Journal of Medical Ethics by Walter Sinnott-Armstrong, a philosopher at Duke University, and Franklin Miller, a bioethicist at the National Institutes of Health. Here is the abstract:

What makes an act of killing morally wrong is not that the act causes loss of life or consciousness but rather that the act causes loss of all remaining abilities. This account implies that it is not even … morally wrong to kill patients who are universally and irreversibly disabled, because they have no abilities to lose. Applied to vital organ transplantation, this account undermines the dead donor rule and shows how current practices are compatible with morality.

The Boston Globe has some analysis of the paper here.