Here's a question for you, then: Would you draw that line just for yourself, or for everybody?
I can understand someone not wanting to throw the switch, certainly. While you may know intellectually that you are helping your loved one, emotionally it might seem like you're killing them. I can imagine many people feeling like that. That's why they want the doctors to do it for them. Or give the patient the means to do it himself.
But legal issues aside, you run smack up against the religious prohibitions against suicide. How many patients would be unwilling to push that button because it would condemn them in the eyes of their Church? Isn't suicide the unforgivable sin?
And you still have the problem of patients who are non-responsive, virtually brain-dead, yet still breathing. They cannot push the button themselves. Could you do it for them?
I've experienced this situation myself. My mother-in-law had a massive stroke, leaving her comatose and all-but dead. The doctors said she would not awaken, and that even if she could there was too much damage. She would be a vegetable. But they could keep her alive indefinitely with a feeding tube.
I didn't have to make the decision, my wife and her father did, but I was asked for my opinion and they made what I believe to be the right decision: they refused the feeding tube. The hospital would provide no food or water, except for the little amount of fluid she would receive with the medication she was given to block stomach acids. We were also told that we could ask for morphine injections if we felt she was in any pain. This was, I believe, the doctor's way of letting us "push the button."
I don't know if my father-in-law realized that, but it doesn't matter because he wouldn't have done it anyway. Neither would my wife. I think I would have, but I can't be sure. It was hell watching her die slowly, even though there was absolutely no indication that she was in pain or aware of her situation. She lasted less than a week.
Ultimately, I think this week was good for my father-in-law as it let him acclimate himself to the idea of her death. By the time she was gone the worst of the mourning was over and we were able to make funeral arrangements in a less emotional state. But I still think she would have been better off if we'd taken the morphine option and ended it quicker. Sitting in her hospital room listening to the Cheyne-Stokes breathing as she got closer to death was about the worst thing I've ever had to experience.