During a middle school history class, the teacher told us about a group of people who, after being shipwrecked, got so hungry they ate each other. Predictably, much of the class started groaning and saying, "Ew!" or "Gross!"
The teacher, who only became cross occasionally, lit into the class.
"Now, look!" he said. "I'm not saying what they did was right, but think about what you would do if you were in that situation!"
Strange that it took the class's resistance to cannibalism for the teacher to admonish us...