I voted "yes" in this debate, but really the straightforward "yes" is too much of an unequivocal answer. The answer should be "it can be". I also believe, which for some might sound very inconsistent, that, although euthanasia can be ethical, it should not be made legal.
The Moral Case
I believe that euthanasia can be morally acceptable for exactly the same reasons I believe suicide can be morally acceptable: people cannot be denied moral ownership of their own existence. Denial of suicide would be denial of the most fundamental freedom in life:the freedom not to continue living. This freedom is essential part of being human. It is the reverse of this other unique aspect of human condition: being aware of our own mortality.
I think that situations in which suicide is morally GOOD are extremely rare. Situations in which euthanasia is morally good are even less frequent. However, sometimes, nay, very often, the moral choice is not between morally good and morally bad, but a choice of lesser evil. Euthanasia can be the lesser evil.
There are situations in which the extent of pain people suffer robs them of all humanity, of all dignity. There are situations in which life doesn't only seem not worth living for the sufferer, but can be genuinely deemed so by most onlookers.
The most clear to me is a last phase of debilitation, terminal illness: it's the agony, which is sometimes stretched over days and even weeks, with even the best painkillers struggling and failing to provide relief, with the body betraying the mind and the spirit that inhabit it. If the person cannot, themselves, obtain means of ending their life, I think it can be acceptable to do it for them, provided they repeatedly expressed a clear, unequivocal wish to that effect.
There are other cases, in which the person doesn't necessarily physically suffer, but his or her mind is gone. They are but the shell of what they were: their mind and spirit are not trapped in a decaying, agonised body, but already gone, disappeared in the flurry of chaotic nervous impulses and meaningless activity of the brain. If such a person is what is called a persistent vegetative state, the decision to end their life is often taken by medical personnel, but if they are seemingly physically functional, as in later phases of Alzheimer for example, the moral problem is profound if they are somebody who previously expressed a clear desire to not to live through such condition. I believe euthanasia is always unethical in such cases. None of such diseases happen suddenly: the early signs usually leave plenty of time for suicide if the sufferer is determined enough.
I believe that the moral decision to participate in euthanasia must be based on the current will of the person being helped to die. I am against so called "living wills", although I would hope somebody would pull the plug on me if I ended up as a so called vegetable.
Even that has a substantial exception, though: the most difficult case, when somebody's suffering is of a mental and not physical nature; but for some reason they are unable to take things in their own hands. I find it hard to imagine a situation like that that would require euthanasia, unless the person is treated as somebody mentally ill or senile. There are, of course, some schools which assume that every suicide is a result of some form of mental illness, that by definition, mental illness is a necessary condition for somebody to decide to end their own life, that there is no "rational suicide". I don't agree. I think rational suicide is possible, but I also think that the line between the two is too thin and the difference often too subtle to make a viable moral case for euthanasia or assisted suicide in such cases.
And finally, the kind of euthanasia that leads to the Nazi associations and fears about genocide, extermination and back door eugenics: euthanasia decided by somebody else, based on the idea that some human beings are not human being enough to be worthy of living. This is the easy one. Without any doubt, this type of action could be never considered morally acceptable.
In all disputes about euthanasia, there is sometimes blurring of the line between euthanasia (actively assisting suicide or killing somebody) and allowing for the natural death by withdrawing or deciding not to start active, medical intervention.
There are many cases in which medicine pushes on, because it can, because it is what it does, because this is what is expected of it, without asking why, to what end and at what cost. It keeps newborns with severe perinatal damage or with known genetic conditions alive-just, to surely die after long suffering in the next few weeks. It insists on pumping people with advanced, metastasised cancer full of chemo instead of teaching them to accept the inevitable. It is such cases where the questions of dignity in death and value of biological life should be asked more often.
All of the above doesn't mean that euthanasia should be legal. The the danger of such law becoming the thin end of the wedge towards increasingly more free interpretation of what is a justifiable case for euthanasia, and the scope for individual abuse by the ruthless and the greedy and for social abuse by the priviledged and the powerful is too great to be allowed.
In countries where euthanasia is legal, despite seemingly complex and fool proof authorisation process, the abuse of the system seems quite frequent. The temptation is too great.
Euthanasia should remain the last moral choice of high principle or the final act of desperate kindness towards the most loved one, even at the risk of persecution, not a legalised process.