Tracy Latimer had CP, just like me. I live in fear of someone, someday, deciding for me that my life is not worth living. Where is the dividing line? Because I can walk, because I can talk, does that mean I'm somehow exempt from someone trying to kill me? Proponents argue that it should only be used with people with the most "severe" disabilities. What defines severity? Functioning labels are arbitrary and absurd. And one person with the exact same capabilities as another may enjoy life far more, for a myriad of reasons.
Not to mention quality of life is not solely defined by internal factors. As I mentioned above, two people with the exact same capabilities (if such a phenomenon even exists in the wide world of disability) could have diametrically opposing views on their quality of life. I postulate the situation of two people of the same age with the exact same disability, exact same capabilities and abilities. One could live independently, with a power wheelchair and lift equipped van, while directing a team of qualified and reliable personal assistants to manage their daily care. The other could still be living with their parents, stuck using a manual wheelchair that they are unable to propel independently, reliant on their parents or unqualified personal assistants for their daily care. They may also be effectively homebound, without a lift-equipped van or predictable public transit in their area. I consider the first person to have a far better quality of life, and these external factors can have a tremendous effect on a person's perception of their own quality of life.
Our perceptions about assisted suicide and quality of life are also heavily influenced by societal and cultural norms. In the Star Trek: The Next Generation episode "Ethics", Worf attempts to convince his friends to assist with his suicide. Because he is a Klingon, part of a warrior race, he sees no honor in his condition, and