Whatever the reason for practicing cannibalism, one cannot ignore the serious health risks associated with with the consumption of human body parts. Eating the brain can result in Kuru, a deadly disease which affects the brain and nervous system, and is just about the human equivalent to mad cow disease. Consuming the placenta is dangerous because it can contain bacteria which is harmful to both the mother and the baby.
With such health risks associated with cannibalism, one cannot condone the practice as ethical for the simple fact that is is a hazard to human life. No spiritual or religious reasons for eating human flesh can outweigh the dangers of cannibalism.