The inquisitions started under Innocent III (c.1100) against the Cathars and at the rise of the Dominican rite... I did not say the Inquisitions were started with Constantine.
That takes us back to the Thirteenth Century and into a feudal order where the Church was only one of the players. Innocent III was one of the few popes who was able to exercise the kind of authority that some think seem normal in papal history, As for the Cathars, are you sure you want to be the champions of a sect that was as different from Christian as the Muslims were? Imagine the Mormons of Joseph Smith but with ten times their numbers? It does, of course, show the futility of suppression. The South of France, where the Cathars were powerful, would be a hotbed of Calvinism and then of revolutionary radicalism. Injustice leaves a stain that lasts generations.