My mother worked in ICU/Trauma for a long time, and said it was always the real crappy families, ie druggie/hooker kids of parents, who would not let their parents go with dignity, but demanded they be kept alive indefinitely.
I do not want to live on a heart & lung machine. Please let me go if I am ever in such a position.
Then think before you give permission to be put on a respirator--no law or moral value requires one to submit to having one of those things installed. There is an abyss of difference between an active "mercy killing" and a simple refusal to be tortured to death by technology.