Update of the update: The conversation continues, 80 comments last I looked, though most of them are worth reading. I made a few more, but I'm done now, my arsenal of weapons of illogical destruction having been exhausted. Zippy shows up a few times and, no doubt about it, he's good. So, eat up. :~)
Update: I threw in my two cents, which goes like this:
All right, Lydia, I'll give it a try. I think I both agree and disagree with Zippy - agree in his analysis of 'object, intent, and circumstances' (though I will use means and ends for familiarity's sake) leading to double-effect, disagree that the definition of cannibalism (as morally wrong) should always include, at a minimum, the consumption of human remains. I think there needs to be more than that latter.
For example, suppose my traveling companion freezes to death after our plane crashes in the Andes :-), and that this happens quickly enough that I have not had time to look at him as an object of use until after he expires. Now, normally it is objectively wrong to eat our fellows as a source of nourishment, for whatever reason (religious,etc.), though in all cases the offender may not be morally culpable for his action, lacking knowledge of why it is wrong. Should Uncle Joe collapse and perish at the family reunion, we cannot all turn to each other and say, "Let's have him for dinner." But can the circumstances in a particular instance change what would normally be wrong into a right, without violating my allegiance to a sworn premise: that I may not use an evil means to a good end? I say yes.
Let me use the hackneyed case of the ectopic pregnancy, in which the doctor must remove the child to save the woman, knowing all the while that 'normally' abortion is, without exception, evil. Does the doctor's action constitute a rationalized exception? No, because (under double-effect) the baby's death is not intended as a means to his end, though he knows the child must die. He is acting in self-defense on behalf of an innocent other who cannot defend herself against an unjust aggression perpetrated by a mishap of nature. Likewise, after due passage of time, it occurs to me that I will certainly starve to death if I don't eat at least a portion of my frozen traveling companion. My end is to survive (which is a good end). The means to that end is eating human flesh, which I would normally consider wrong, but circumstances have changed that. I am acting in defense of my life. It's not as though I'm throwing someone out of the lifeboat that the rest of us might sail to safety without worry of sinking. I intend no harm or disrespect to my frozen fellow. Any harm suffered has already been done to him by a freak accident. If a case can be made that any harm comes to him or to me by my eating him, that harm is an unintended side-effect subsumed by a greater good - the obligation to preserve my life.
As to harvesting organs from dead bodies, I agree with Zippy about the conflict between practice and principle. Live-donor organ transplants I have trouble relating to the proposed conundrum at all, since to me it seems one of those line-drawing problems with which we are so familiar (e.g., defining obscenity - "we'll know it when we see it.") If your loved one needs a kidney, that's somewhat different than asking for your eye, since without the kidney he might not live, whereas blindness does not result in death. In true cannibalism, the one being unjustly attacked for the purpose of evisceration has no say in the matter (i.e., it's being done against his or his proxy's will). This does not appy to the live-donor situation.
In sum, unless the cannibalism in premise 1 (which you don't want to argue about) is not strictly defined, premise 2 may well be undefeatable.
So, uh, whaddya think?