I personally believe that this should be legal, but I do not believe that it is compatible with our current, and often hypocritical, legal consideration for human life.
This question is difficult because it depends on many multifaceted definitions; what do we mean by legal, and what is the bearing of legality upon morality? Are all laws moral? Are immoral things always illegal? Exactly how much assistance would the physician be allowed to render? Does the person get to choose their manner of death (imagine if someone wished to die by being shot)? These are important questions because, as is often seen in legal matters, the way in which the act is defined as legal or illegal often depends upon a significant amount of context.
The problem here, I believe, is that our context is fundamentally skewed. We cannot have a consensus because we have not established a legal value of life nor a legal authority over life.
Consider the contradictory laws on human life that are currently in place:
- Murder is illegal, but killing in war is legal
- Abortion is legal, but only under certain circumstances
- The death penalty is legal and is not considered murder
- Attempted suicide is often treated as a result of mental illness
An anecdote on this last point: I once spoke to a psychologist who said that, at least on older tests, considering suicide under any circumstances including hypothetical ones was a warning sign of insanity, because "the healthy mind would never think of killing itself".
Legalizing assisted suicide would require us to acknowledge that it is possible for a sane person to seek death (or to broaden our interpretation of sanity to include things that were formerly considered insane). As it currently stands, the individual does not actually have control over their own life at any point in their lifetime; there are ways of legally killing someone at any point in their life, but no point at which the person may legally or "sanely" decide to kill themselves. Some have pointed to this as an inherent but subtle support for violence and murder in our legalistic outlook, as well as an unsustainable "life fetish" which values being biologically alive over the quality of the life itself.