I always find these discussions very interesting. I am a registered nurse who works on a medical ward for the elderly, and I did 3 years of training so I have witnessed death in many different situations. From my experience, I don't really think there is a "humane" death. Maybe humane is the wrong word, but death is very far from dignified. I have witnessed death from unexpected cardiac arrest, painful deaths from cancer, painful deaths from various co-morbidities,"peaceful" expected deaths and sadly, even suicide. There was nothing dignified or humane about jumping up and down on someones chest, nothing humane about people screaming in pain and constantly agitated from their co-morbidities, certainly nothing humane from a drowned body and even a peaceful death is not dignified. When you die, your body relaxes therefore you expel waste from various orifices. Then us nurses have to perform last offices. We do try our very best to make it as dignified as possible, carry out last wishes from patients and families but there is nothing worse than trying to dress someone when they are stiff from rigor mortis, you do have to be quite rough at times. This is my view on death in general, that it is not the most dignified experience people would like it to be. For some, this may not be an issue. You would be dead, you would not have to experience this. But for me, I hate the thought to be laying there naked while I was being tugged about covered in my own shit and piss while some nurses cleaned me up and shoved me into a body bag.
Another point I would like to make is that some physical illnesses do turn out to be terminal, such as cancer, MS, parkinsons, dementia etc. The body eventually shuts down, people cannot control the path of these illnesses. Yes, medically we can try to prolong life as much as possible, however, death is sooner rather than later. I may get flamed here, but with mental illness, although it can be a chronic illness for many, it is NOT a terminal illness. In the end we have that choice whether we want to live or die (regardless of the emotional pain which can often make us feel we have no choice, but ultimately suicide is a choice). Those who commit suicide die by their own hand. Although for many of us, our conditions will not be cured, it can be controlled, managed via different means but physically it is not going to kill us. There would also be an argument as to how rational ones mind is at the time they commit suicide, but that is another argument for another day. This is why I do not believe in euthanasia for those will mental health illnesses. Although for some, few may be the exception, completely rational but for many there is hope of control and even recovery of their illnesses.
I have also read some people's point at keeping the elderly alive brings in the money. Well I have to say that this is far from the case. Even the most simplest of care packages for the elderly (an emergency call bell, a carer a day etc) is so expensive. There is both the medical and social care aspect to consider, not just how much money drug companies reel in from the drugs these people need to stay alive. It's expensive, so expensive and yet care is most lacking in caring for the elderly. In my opinion, prisoners are treated better than some of our elderly are and it breaks my heart.
I may have gone slightly off the point, but wanted to throw those things out there that people may not have considered.