The jedi are good sith are bad

Why can't people understand this? Where do people get these stupid ideas that jedi are evil/sith are good? 5 year olds can understand that sith are bad jedi are Good yet some adults can't. George lucas himself has said its black and White good vs evil story. But but jedi are not perfect and they have made mistakes so? How can anyone even compere that to what the sith do?