I think that would be very selfish. I would not want my loved one to suffer any longer than they wanted to and would totally be ok with them not staying alive. My grandmother and mother both suffered A LOT at the end, and my grandmother continued to say she wished she was dead and even refused to eat but they kept her alive anyway until her legs got gangrene and my parents had to sign a form saying they did not wish to amputate her legs and let her die ( she was 96 at that age) and I am thinking to myself, oh hell no, I am so not getting to that point....
Pearl made a very good point, why do we put animals out of their misery and not humans? Especially if they WISH to die. My grandmother did not have the option to do it herself, she was paralyzed after a stroke and couldn't walk.