The official ecclesiastical procedure against heretics indeed had its excesses, but events from hundreds of years ago should not be judged by today's standards. To understand this, let's look at the formation of the Inquisition. The heretics of old (Cathars, Waldensians, Bogomils, Hussites) were far from being pious religious dreamers. They burned down churches, cities, killed people, and lived or propagated abnormal civil and sexual lives. The state had to act against these actions. When the state began using the accusation of heresy for political purges, the Church intervened and did not allow the state to arbitrarily decide who was a heretic and who was not. Thus, the Inquisition saved many people's lives, but history books do not write a word about this.
The perception of the Inquisition's scale and methods is also unfair. Many have been led to believe that the Inquisition massively and easily burned people at the stake, while subjecting them to terrible torture. It is true that torture was used in certain cases, but this was due to the spirit of the times, and the Church practiced mercy here too: The inquisitorial court used one kind of torture, while the secular courts' torture instruments were only limited by imagination. It's not without reason that many caught criminals invented a religious element in court ("the voices said"; "God messaged") so that their cases would be transferred from the secular to the inquisitorial court, where they could hope for a milder punishment. Thus, the majority of inquisitorial trials were ordinary criminal proceedings, and not "dramatic collisions of conscience and power." Death sentences were only issued in severe and common-law cases. The number of these was not more than two or three individuals per year. The severity of punishments is also relative. Indeed, the punishments were harsh. "But the medieval person could endure them. In less softened peoples today, the justice system still uses more cutting methods" (Tamás Mehrle O.P.: The teachings of St. Dominic's life).
True religious judgments were rare, and only very significant or particularly violent heretics were executed (e.g., Jan Hus). However, two factors come into play here. In the Middle Ages, God was considered the King of kings. Anyone who offended the king was sentenced to death for treason. Teaching heretical errors about God or falsifying His word was thought in the past to offend the King of kings, thus heretics were also sentenced to death. But remember, in the Middle Ages, Christianity was the state ideology, the main force of social cohesion. Attacks against it violated societal interests. Open critics of the state ideology were always punished. It's no different today: And it's not necessary to think only of the mass executions of the Great French Revolution, the Nazi concentration camps, or the communist gulags. Just observe the activities of national security agencies. In many Western countries, if someone is a mover of a movement considered "heresy" by the official medium, then the state power monitors and possibly shuts it down. Not without reason. Modern freedom of speech is not as straightforward as many believe. In many European countries, openly or even covertly offending certain nationalities or deviations is punished with imprisonment. The essence doesn't differ much from the persecution of heretics, and the methods are not far from those of the Inquisition.
Spain is an exception. Not only because the Inquisition operated most harshly there, but because there, the Inquisition was primarily in the hands of the state, not the church. This led to many abuses and mercies, but fundamentally, there was a reason for it. Spain was full of seemingly converted Moors who pretended to be Christians but were actually spying and trying to bring Europe under the crescent. These people were indeed sought out by all means. However, it's evident that the Inquisition also served a counter-intelligence function here. Its name reflected this: Sanctum Officium Inquisitionis, the Holy Office of Investigation.
So, the Inquisition had many dark sides, but these were not the consequences of the institution itself, but of human fallibility. It stands that the sanctity of the Church is not diminished if some of its members commit sins, because such scandals are unavoidable. If the inquisitors operated conscientiously, they cannot be faulted, for with their rigor, they protected the common people from common-law, religious criminals. There were saints among them.
Many believe that "the Catholic Church burned at the stake those of different faiths."
First of all, it was not simply "people of different faiths" who were burned, but rather the incorrigible rebels and deliberate religious subversives. Second, and most importantly, it was not the Church that burned them. The Church itself never burned anyone, either at the stake or otherwise. Death by burning is a terrible remnant of pagan Germanic law, which unfortunately, was adopted and maintained by virtually every state in the Middle Ages; and importantly, it was a state punishment, not an ecclesiastical one. Just because the state was so intertwined with the Church at the time and considered religious crimes as also state crimes: qualified as subversion and rebellion, hence sometimes the state power itself pursued the perpetrators of religious crimes with its often brutal means, including torture and burning at the stake. In determining the religious crime, ecclesiastical factors were of course consulted, and thus mixed courts were established, such as the Inquisition. The ecclesiastical factors unfortunately erred in often being too readily defenders of state excesses and not sufficiently opposing the cruel and often unjust methods of torture and punishment. In most cases, however, they did take action and it was the Church itself that repeatedly and vehemently spoke out against these barbaric customs.
In distributing death by burning, everyone was equally guilty at the time: individuals, society, the people, cities, and states, not least the heresies themselves, which also extensively used torture and other forms of torment against Catholics.
Many also believe that "the Inquisition led hundreds of thousands to a horrendous death."
The "hundreds and hundreds of thousands" is a mild exaggeration invented by the Spanish apostate Llorente and circulated by numerous fanatical anti-Catholic novelists. According to serious calculations, the number of victims of the Inquisition over 700 years falls well short of even the number of martyrs and those tortured during the English persecution of Catholics. Why do those who so readily mention the Inquisition remain silent about the much bloodier persecutions of Catholics in non-Catholic areas?
Moreover, the Inquisition itself was only partly an ecclesiastical institution, as we have already explained. It should also be added that the best-performing Spanish Inquisition was a state institution, established to monitor and neutralize the traitorous dealings of Arabs who remained in Spain after the long Moorish occupation and had ostensibly converted to Christianity, as well as the Jews who secretly allied with them. To this end, the judges of the Spanish Inquisition always first sought to determine whether the suspected Arabs and Jews could legitimately claim their baptismal certificates, that is, whether they were indeed living a Christian life or merely using baptism as a cover. This led to a unique mixing of religious and civil elements in the Spanish Inquisition. The Church cannot be held so responsible for the Spanish Inquisition to the extent that, on the contrary, it was the Roman Curia that protested against the actions of the Spanish Inquisition in many cases, seeing them as an unwarranted interference by the Spanish crown in ecclesiastical legal matters.
But what does the world know about this! The "Spanish Inquisition" is a hobbyhorse on which the enemies of the Church have happily ridden for a hundred years. Experts can refute the horror stories circulating about it a hundred times, but for some people, what matters is not whether something is true, but whether it can be used as a trump card against the Catholic Church.
In 1590, Antonio Perez, the private secretary of Philip II, fled to France and then to Germany due to murder and treason charges. While there, he wrote a detailed report for the Protestants about Spain's deeds. But in revenge, he added two or more zeros to every number, thus inflating the number of victims to several million over a hundred years. The countries of William of Orange and Elizabeth I enthusiastically spread these writings that discredited the Spanish, which became known as La Leyenda Negra - The Black Legend. This, in turn, spread in the public consciousness through Anglo-Saxon historiography and has become indelibly embedded. Since then, no one has ever done so much harm to their own country.