What is the moral lesson of Ali Baba and forty thieves?

The author of the story says that good people will be saved from poverty and bad people but bad people's power and their riches never last long and they will meet the miserable end. This is the moral. The author had forgotten one thing, Alibaba (hero) becomes rich by the booty of the thieves therefore Alibaba too had become a thief. This is a children story. I think most of the authors who wrote children stories never paid more attention on the subjects.