Cannibalism should be a last resort. If it comes to it then yes, cannibalism can be necessary but it depends if the person you are eating, gives permission. (assuming they are not dead before) When people are on the brink of death, they will do anything to survive, even if it comes to killing and eating each other. Other eating themselves.
If the world ever came to this, the world would be at its end. But, with that said, I say yes. I don't care what anyone says, i believe that if someone had to watch there loved ones suffer and diminish right in from of their eyes, i think that could drive a person crazy enough to push them to eating human kind, or do anything for that matter.
In a truly ideal world, cannibalism would never need to happen. In that same world, not a single person would ever want for anything. Sadly, the world we live in is filled with disparity. The weakest of the group tend to fall by the wayside. Cannibalism is an extreme act but if your survival depends upon eating a fellow member of your species or die, you will eat them.
The only time cannibalism would be needed is in a case of survival. As with the previous opinion, such a thing is only to be used as a last resort and obviously killing people to eat them is never alright. People can push themselves to do all sorts of things when their on survival is at stake.
I believe in extreme survival, life and death situations, humans must do what they have to do to survive, including cannibalism. For example, the rugby team that crashed in the Alps years ago had to resort to cannibalism in order to survive their ordeal as food had run out. I don't believe that people should be killed to be cannibalized, but in those disasters where it is the last resort I believe it is ok.
Our human psyche allows us to make thoughtful choices and to realize the beauty of the human mind and existence beyond foraging. I argue that eating another human being no matter what the reason devalues our position in the universe and makes a human less than he or she is.
Cannibalism is never necessary. There is no reason to eat another human being and there is no way to justify it either. It is absolutely disgusting and should not be done. Just saying that someone ate another person sounds disturbing to me. There is no time or place where it is appropriate.