Prepare for some intellectual heavy-lifting.
Steven O'Shea's Friar of Carcassonne is a well-written scholarly tome that examines the roots of The Inquisition, tracing its origins in large part to religious and secular outrage directed at Brother Bernard Delicieux, a well-intended Franciscan friar whose contentious rabble-rousing fanned the rage-filled embers of papal ire into a burning funereal pyre.
Although much of the firebrand Franciscan's life is lost to history, a remnant of Brother Bernard's existence remains written in the record of his own inquisition by Jacques Fournier, the portly Bishop of Pamiers who would later become Pope Benedict XII. Upon this mention, the author largely bases his account of the Friar's legacy: his quest to end Rome's unjust imprisonment, torture and inquisition of its perceived enemies, which -- in the end -- grew to include the titular Friar of Cascassonne.
O'Shea's Brother Bernard is a master of political manipulation, using his gift for oratory to influence the French king (Philip the Fair) and his emissaries, and incite near-riots among the people of Carcassonne; while defying bishops, inquisitors, and even the papacy, to which, hierarchically, he should have been subject. No one was beyond earshot of Brother Bernard's railing, and his diatribes were not always well-received. He offended secular and religious authorities alike.
He also at times showed a shocking lack of emotional intelligence, pushing his argument a bit too far and, consequently, alienating allies: A one-time protector, King Philip eventually abandoned the Franciscan friar in an effort to reconcile with Rome; and later found himself the target of treasonous intrigue, when Brother Bernard appealed to a lesser princeling of Majorca to help Carcassonne secede from France. (The plot failed before it began when the King of Majorca, upon hearing of his young son's involvement, beat the tar out of the princeling and sent Brother Bernard packing.)
Eventually, having lost the protection of the King, and at the mercy of the Pope, Brother Bernard found himself imprisoned among the heretics, charged on multiple counts -- initially, a list of 40 offences, that was later expanded to 64. Largely, these can be categorized into four areas: (1) obstructing the inquisition; (2) high treason; (3) adherence to heretical notions of poverty; and (4) the murder of Pope Boniface VIII through black magic. Eventually, he was found guilty on two: obstructing the inquisition and high treason (for having asked the Majorcan prince for help in seceding from France). Brother Bernard died, imprisoned in the same prison that he had fought to have emptied, in 1320.
Ironically, far from ending the brutality of Roman inquisition, Brother Bernard's uprising seems to have only seeded the field for the expansion of the practice into a full-blown terror recognized as The Inquisition of Jews and others branded as heretics.
A couple of items that I feel should be noted here:
(1) This is not an exhaustive, nor even a cursory, look into Catharism, a religious belief system that meshed together various Christian beliefs with gnostic views. It was considered heretical for good reason: Cathars believed in two gods -- one good and one evil. (In their belief system, the "good" god of the New Testament created spirit; and the evil god of the Old Testament created matter, all of which was evil.) Cathars believed that humans are angels, trapped in material bodies, destined to be reincarnated until they became perfect, by dying in a state of consolamentum, in which all sin was forgiven. (If they began to recover from near-death, they were smothered or otherwise killed by other Cathars to ensure that their souls would not have to be reincarnated again.) They did not believe in sacraments -- including marriage (because all spirit is genderless) -- or procreation. While calling themselves Christian, Cathars held beliefs are most certainly unbiblical; and the Roman Catholic Church, as sole dispensers (at the time) of Christian teaching, would certainly become enraged at the misappropriation of Christ, which they would see as endangering other believers' souls. (I'm not excusing the actions of the Roman Catholic Church, which are heinous. I am merely explaining here how RC would damn the Cathars' views.)
(2) Brother Bernard was not completely pure in his zeal. He lied when he felt it was necessary to escape punishment. He manipulated, inflamed, and used men whom he found useful. And he did have a book of black magic in his possession. This is a particularly interesting happenstance as his adherence to Spirituality demanded that he have few personal possessions. Why would such a book hold so much value to a Christian monk? It's particularly disconcerting given that the book contained spells and recipes for poisonous potions -- which well could have been used to murder his enemies. (Two popes, whom Bernard predicted would soon die, did expire quickly after his pronouncements.)
Highly recommended to those who are students of Church History and Politics, O'Shea's Friar of Carcassonne is an eye-opening investigation into the roots of The Inquisition.