The idea of assisted suicide is a very, very slippery slope in my opinion - not that I don't approve of people having the right to make their own choices as to when they've had enough, but it could lead to lawmakers and other people in positions of power deciding that people with certain conditions or with a certain degree of severity are not worthy of being alive based on some subjective measure of "quality of life". We've already seen it, with disabled people (particularly developmentally disabled people) being denied heart transplants, kidney transplants, etc. because doctors feel that the lives of non-disabled people are more worth saving than disabled people. I'm very scared that the personal choices of disabled people will be co-opted to make assisted suicide a choice on the part of others "on behalf" of the disabled person. Again, it's already happening. Robert Latimer, who murdered his daughter Tracy in 1993, told police that he could not bear to watch his daughter suffer. The judge who exempted Latimer from the minimum sentence for second degree murder called it "compassionate homicide".
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 desires to die. It is ingrained in his culture that Klingons must be physically strong, honorable, and able to fight. Although not quite to that extreme, our society has a similar credo. One of the biggest myths in our society is the myth of independence. Our culture pushes the narrative that we must pull ourselves up by our bootstraps, rise from the ashes of adversity by the skin of our teeth. Anything less is seen as weak - and weakness is taboo. In fact, the Klingon society, or at least those morals, can be seen as a hyperbole of our own society, which prizes physical strength and muscularity. These ethics can even be seen in the reflection of our own thoughts and decisions. Shin, for you, you say the dividing line (at least part of it) is not being able to wash yourself or feed yourself. I was not able to shower myself until at least age 15, and needed someone to help me get out of the bathtub for a time after that. Despite that, I had a fine quality of life. I know people who can't dress, shower, or feed themselves and still have a fantastic quality of life. I realize, of course, that each person's definition of "quality of life" is different, but it seems to me that our fears about what will happen when we can no longer take care of ourselves stem from a society that prizes self sufficiency above all costs.
Assisted suicide is a complex issue, with many different facets. I urge both British and American citizens to think about assisted suicide in a new way - how can we make our lives better, instead of our deaths? Maybe if we improved the experience of life, so many people wouldn't be seeking the option of death.