Answer by Balaji Viswanathan:
One the one hand you have a drunk driver who stupidly drove a bus off the bridge and killed 50 people.
On the other hand you have a psycho who tortures & kills his victims in a cruel way. He deliberately seeks one group of people – say girls of certain age – and does horrors to them. Let's say he killed 12 such people.
Who will you fear the most? The drunk driver did kill 50 people out of sheer stupidity. But, he had no intent to drive off the bridge. He is a criminal no doubt, not necessarily a psycho. The second guy on the other hand might have killed only a fourth as much but could still send down shiver in other's spines.
That's the difference between Mao & Hitler.
Of course, movies do help understand Hitler's crimes better than others. However, it is still a minor point. By no stretch of imagination is Mao is a Hitler.