Why was the French Revolutions idea of everyone having rights and being equal, a dangerous idea?

Why the French Wanted Equality

The nobles and clergy were the privileged orders. They were exempt from such direct taxes as the taille, or land tax. Most taxes were paid by the Third Estate—a class that included peasants, artisans, merchants, and professional men. Even among these groups taxes were not equal

Explanation:

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the hereditary right of a monarch to rule from the mandate of heaven