There is something obviously troubling in this way of thinking about crimes against persons. Indeed, the most abominable practices, proscribed in virtually all societies, are not excused by consent. Incest, even between consenting adults, is still incest; cannibalism would not become merely delicatessen if the victim freely gave permission; ownership of human beings, voluntarily accepted would still be slavery. The violation of the other is independent of the state of the will (in fact, of both victim and perpetrator).
The questions can be put this way: Is the life of another human being to be respected only because that person (or society) deems or wills it respectable, or is it to be respected because it is in itself respectable? If the former, then human worth depends solely on agreement or human will; since will confers dignity, will can take it away, and permission to violate nullifies the violation. If the latter, then one can never be released from the obligation to respect human life by a request to do so, say from some who no longer values his own life.
This latter view squares best with our intuitions. We are not entitled to dismember the corpse of a suicide nor may we kill innocently those consumed by self-hatred. According to our law, killing the willing, the unwilling, and the nonwilling (for example, infants or the comatose) are all equally murder. Beneath the human will, indeed the ground of human will. is something that commands respect and restraint, willy-nilly. We are to abstain from killing because of something respectable about human beings as such.
Leon R. Kass – Life, Liberty, and the Defense of Dignity: The Challenge for Bioethics p.238