I've never really participated in the discussion, but in my opinion it all boils down to whether we (the person making the decision) believe in the existence of God - or not. If anyone involved believes in God, he should be allowed to act according to his faith. Again, that is based on the assumption that there are universal rights and obligations - for which God is the only real basis. Since we cannot prove otherwise, it should be taken as granted that we do have the right to control our own thoughts and bodies, and the obligation to grant the same right to everyone else.

To be clear; our decision should be based on our beliefs, but the significance of our decisions depend on Gods existence. If there is no God and we are just matter, nothing ultimately matters. If God exists, we seem to have an obligation to do what we can to extend the persons life. If no-one involved believes in God, they are collectively free to do as they see fit. But if even one involved believes in God, he should have a VETO right. Unless the others give him that right, they effectively give him permission to kill them all. Not that someone would actually do that.