But again, as any system can be abused, I do not consider this suspicion grounds to base policy. I merely note that it cannot casually be dismissed as a "boogeyman," and that any system of assisted suicide must have some proper protection to eliminate the likelihood of abuse.
My second reaction is a reflection of a religious nature: why God does not permit suicide as understood in the traditional Jewish framework, as understood by me.
Central in traditional Judaism is the notion that the human body is made in the "image of God" (whatever that means) and is on loan to us while our soul dwells therein. Indeed, the return of the soul on awakening is a miracle for which we daily thank God first thing in the morning after washing the hands and emptying the bowels/bladder. Most folks familiar with this principle tend to dwell on all the positive aspects that blend so nicely with modern western thought. e.g., the basic dignity of man, the duty to respect one another, and so forth.
Few, however, prefer to dwell upon the flip side. This Body Is Not Yours To Do With As You Please. It is only a loaner and comes with a rather strict licensing agreement. Indeed, in halacha (Jewish law) we have a large quantity of inexplicable law that amount to apparently arbitrary limitations on what you can do with the physical body on loan to you. No tatooing it. No shaving the head bald. If male, lop off the foreskin at 8 days -- PRECISELY at 8 days (unless prevented for health reasons). Restrict what you put into it to a limited set of foods (with meat and birds must be slaughtered in a specific way), and cannot be mixed with dairy. No pooping in camp. The law dictates with whom you may not have sex, and when you may not have sex. It even dictates things you must wear (phylacteries if male and over 13) and what you cannot wear (wool and linen).
It is in this context that I understand the prohibition on suicide. Suicide is the ultimate act of rebellion and arrogance against God's authority over the physical body given me and inhabited by my soul. It is a statement that I, not God, shall exercise my free will to determine the hour of my own death. That I, not God, shall decide when and how to terminate this aspect of my existence. While the halachot around such questions of when I have a right to refuse care are complicated, there is no doubt that a conscious decision to take affirmative action to terminate my life is prohibited as an act of monumental egoism utterly inconsistent with the conception of dignity due to the body lent to me by God.
Prachett's desire to set the terms of his own demise and "shake hands with death" on his own terms is utterly consistent with modern western thought and its central focus on the autonomy of the individual, which makes it utterly foreign to the central notion of traditional Judaism which places God at the center.