There were so many unfair differences between the clergy, nobles, and peasants. The peasants had to pay taxes although they were the ones who really needed the money. The also payed taxes though their vote was not accounted for which should not be fair under any type of constitution document.
By 1789, the French monarchy was way too excessive while commoners starved and froze to death. Just look at the Palace at Versailles and the Louvre as signs that French kings spent way too much money and had way too much time on their hands. The French Revolution was well grounded in the fact that the people had had enough. Unfortunately, the events of 1789 begat another despot who nearly conquered all of Europe. Napoleon Bonaparte was almost as bad as the monarchy he replaced.
The common people were starving and faced series after series of harsh taxes from the nobility. The King and Queen of France didn't demonstrate any regard for the poor conditions of their populace, instead spending huge amounts of funds on war and pleasure palaces. Given the poverty and poor conditions under which they lived, a revolution was justified.
The First and Second Estates undeniably spent more money then they deserved, but the "revolution" wasn't totally justified, they censored arguments against them just like the aristocracy did. They executed people who didn't agree with them. It was basically switching from one extreme to another. The revolution destroyed, not changed history. It accomplished its goal, but did so in brutal ways.