Despite its popularity, I am of the belief that its existence has not been wholly positive; indeed, it has been significantly negative. This much can be learned by examining the history of the Catholic Church, through various events and organisations within the Church itself, which have indeed been responsible for the oppression and deaths of many. I shall spend the remainder of the argument attempting to prove this to you. Note that I shall not cover the entirety of this topic area, only the most notable examples.
Also, it may be worthy to note that I was a practising Catholic for over 10 years, having been baptised as one and received Holy Communion, and thus I have experienced the Church first-hand.
The Crusades
The Crusades are perhaps the most famous (and most commonly referred to) example of the Catholic Church's "evil". The First Crusade (named as such for being the first in a series of eight crusades) began primarily because of the Islamic oppression of Christians in the Middle East (subsequent to the conquest of Jerusalem by the Seljuq Turks instead of the initial Islamic forces that conquered it in 637 A.D.), which involved acts such as the desecration of sacred places (indeed, the Church of the Holy Sepulchre was destroyed in 1009 A.D. and eventually rebuilt, but still fell victim to Islamic attacks).
A request for help from Alexios I (Byzantine Emperor) and the resulting Council of Clermont was enough to set the First Crusade in motion. A series of interesting, albeit irrelevant, events occurred which culminated in the Prince's Crusade in August 1096. The Crusaders swept across Seljuq territory, capturing various strategic points such as Nicaea and Antioch (the Muslim inhabitants being massacred after the successful Crusader Siege). The most important part, however, is the siege of Jerusalem (or more importantly the aftermath). After the successful assault on the Northern Wall, the crusaders finally entered the city, and a bloodbath ensued.
The actual number of deaths from the Crusader massacre of Muslims is unknown, although it is safe to estimate a number around 10,000 (one Arab historian even estimates it at 70,000, although this is obviously exaggerated). My point? My point is that the Crusaders, under the belief that "God wills it", slaughtered thousands of "infidels" inside the walls of Jerusalem rather than demonstrating the mercy that their religion teaches. This wasn't the only instance of crusader brutality for the sake of the Church (for example the massacre of 3,000 Muslim prisoners at the hands of Richard "the Lionheart"), but it is certainly sufficient to demonstrate my point.
Suppression of Science: Copernicus and Galileo
Nicolaus Copernicus was the first man to challenge the Geocentric Model of the cosmos first established by Ptolemy with a new hypothesis: the Heliocentric Model, i.e., that the Earth orbits the Sun and not vice versa. His fully-formed hypothesis was first presented in his book "De revolutionibus orbium coelestium" or "On the Revolutions of the Celestial Spheres". It is worth noting that whilst Copernicus' heliocentric model was a great improvement on the Ptolemaic model, it still retained many of the Ptolemaic inaccuracies such as circular orbits.
However, Copernicus never was persecuted for his theories; he died shortly after the book was published, and never explicitly stated that the theories contained within his book were actually his beliefs. Galileo, however, was another matter. He took inspiration from Copernicus' "On the Revolutions" and wrote "Dialogo sopra i due massimi sistemi del mondo" or "Dialogue Concerning the Two Chief World Systems", despite being ordered to not "hold, defend or teach" heliocentrism. After being published in 1632, the Pope ordered that the publication of any more copies of Galileo's "Dialogue" be stopped.
"Dialogue", whilst written initially to approach the two Ptolemaic and Copernican systems from an unbiased standpoint in order to present them equally (and thus not upset the church), was distinctly pro-heliocentrism, even going so far as to insult the believers of geocentrism. In other words, instead of presenting his work hypothetically, he phrased it as if he believed it.
Galileo's guilt had been decided by the Inquisition, the guilt that he now held for presenting views that didn't fit in with the doctrine of the Catholic Church. After delaying for as long as he could, he arrived at Rome and was tried by the Inquisition. Obviously found guilty, his sentence was that "Dialogue" was to be placed of the Index of Prohibited Books, he was placed under house arrest, he could be arrested by the Inquisition and ultimately, he had to admit that he was wrong and that the Church was right.
Galileo's "Dialogue" remained on the Index for a further 200 years, a time in which the incontrovertibly false geocentrism continued to be taught as a universally accepted principle. 200 years in which a scientific theory was suppressed because it contradicted religious dogma. And the theorist, who presented his beliefs, was persecuted and threatened with torture by the Inquisition. This, of course, leads me nicely onto my next point...
The Inquisition
Their chief weapon was surprise...
No, don't worry, I'm not going to turn this OP into a Monty Python sketch, and instead I shall be discussing "The Inquisition", which had several incarnations, beginning with the Medieval Inquisition, followed by the Spanish Inquisition, the Portuguese Inquisition (created at request by Pope Paul III because of the rising Jewish-convert immigration from Spain) and finally the Roman Inquisition.
Whilst being separate incarnations, the four implemented similar practices and held similar aims; namely, to combat the "heresy" that was becoming prevalent in Europe. The initial Inquisition was created by Pope Innocent III as a response to the heretical sects like "Catharism" in France, which in fact led to the Albigensian Crusade.
The Inquisition had the right to interrogate anybody, and employed several methods in order to identify heretics. The guilty would have to perform an "auto de fe", or Act of Faith. However, those who confessed would be given more lenient punishments such as pilgrimage, although those who were found guilty but refused to confess prior often received corporal punishment, and were occasionally burnt at the stake. Torture was sometimes employed in order to attain a confession, which may have involved waterboarding.
The Spanish Inquisition is perhaps the most famous of the separate Inquisitions. Their primary purpose was to prevent "conversos" (the aforementioned Jew-Christian converts) from reverting to their heretical Jewish practises. Forced conversion was frequently administered to Spain's Jewish population, prior to the mass expulsion of Jews from Spain. Muslim converts, also known as "Moriscos", were also persecuted.
As well as attempting to combat heretics and their practices, the Inquisition also censored and prohibited books because of their content, one of the most notable examples being Galileo's "Dialogue" which I mentioned earlier. Several of these "Indexes" were compiled, each containing their own set of prohibited books. Spain's slow transfer to "the Enlightenment" can perhaps be partially attributed to the Inquisition's hindrance of scientific progress.
The total death toll of the Inquisition is unknown, and a wholly accurate figure is nearly impossible to estimate; however, it is safe to assume that tens of thousands of people died at the hands of the Catholic Inquisition.
Medieval Corruption: Indulgences, Relics, and the Manipulation of the Masses
In 1215 Pope Innocent III issued a decree that prevented any "unauthorised" versions of the Bible. This, interestingly enough, encompassed all of the non-Latin translations of the texts. The purpose of this was simple: to prevent the common man from reading the Bible for themselves, as Latin was a language that only the well-educated could read, and thus the Church could teach whatever it wanted, really. A key teaching emphasised because of this was the idea of a "Hell" and "eternal damnation", which would serve to terrify the masses (thus ensuring Papal control) and indirectly provide funding for the Church.
The Church's funding was secured through various means, one of which being relics. The Church quickly began to teach about the holiness of certain artefacts and locations, and how one's penance could be earned by making a pilgrimage to the location of these sacred items. However, the Church took advantage of this and charged the pilgrims to visit these relics, despite the relics not actually being "true relics" and rather medieval forgeries. Some notable (and rather humorous) examples can seen be through Frederick I of Saxony, who possessed a "Piece of the Burning Bush" and a "Vial of Milk from the Breasts of the Virgin Mary" among 33 pieces of the True Cross.
Perhaps the most notorious concept of the Medieval Church was the idea of "Indulgences". These were essentially pieces of paper signed by the Pope or some religious authority within the church that promised a reduction of one's time spent in Purgatory. Purgatory, an exclusively Catholic concept, was the idea that one had to spend a certain number of years in a space between heaven and hell: in which one must receive a "purification" before they ascend.
Indeed, indulgences should shorten the amount of time one would spend in purgatory, and could be attained for yourself or your family members (usually deceased). The only way in which someone could attain one of these, of course, was by buying it from the Church. By promising a shorter time between purgatory and heaven (and in extreme cases bypassing purgatory altogether), the Church tightened its grip around the populace and their wealth, thus ensuring its dominance up until the Reformation Period.
To be honest, I've merely touched on the subject. I could go on about various areas such as the Witch-hunt and the Catholic Persecution of Jews, but I believe that my point has been sufficiently made.
The Catholic Church has dominated European history for several centuries through war, the suppression of science and alternative religious interpretations, and most of all, by threatening the masses by promoting ignorance, which in turn allows for the complete doctrinal control and manipulation of millions of Europeans.
Would the world have been better had the Church never existed? I can't say for sure; but hopefully, after reading this, you'll be able to see that the Catholic Church we see today was built on the principles of manipulation, ignorance, and oppression.
