cannibalism and the Necessity Defense

In Regina v. Dudley & Stevens (1884), two sailors faced murder charges because they had killed and eaten one of their own fellow sailors (a cabin boy) after a shipwreck had caused the sailors to be adrift in a lifeboat for three weeks without food or water. A passing ship rescued the remaining three English sailors from the lifeboat as they were on the brink of death from thirst and hunger (one sailor turned State's evidence and testified against the other two).

Assuming that the sailors would have died if they had not engaged in cannibalism, should their conduct be excused on grounds of necessity? Give reasons pro and con.