Genuine Gnosis and Gnosticism never died, it has always been practiced quietly by the 'chosen few' in every part of the world ~ the genuine Mystics/Gnostics, the true lovers of God ~ even though evil religionists have always persecuted them and tried to wipe out the Truth. The Truth will never die, no matter what the religionists do.
If you are a Catholic, what do you feel about your loving church persecuting, torturing, and burning so many people throughout history merely because of their beliefs?
PLU 
This is overly simplistic view of history.
It is interesting how it is PC not to judge other cultures but its fine to judge Catholics in the Middle Ages. But we should keep in mind that we now live in a democracy and cultures in the past did not.
In our culture, we elect our leaders. Our leaders can justify their rule by appealing to the last election. This keeps those who oppose their rule at bay, at least until the next election, where they could possibly receive enough votes to overthrow the current power peacefully.
But this way of maintaining order is just a couple of hundred years old. Even before the inception of Christianity, emperors appealed to their divinity to maintain their rule over the people. Possibly emperors themselves thought it was silly for anyone to think of them as gods, but they went along with it because it kept order. After all, who would revolt against a god?
When Christianity came, the emperor was threatened by it. If, as Christianity was saying, that the emperor was not god, then why should anyone obey him? Since this threatened his authority, the emperor would persecute them (It is interesting that we have no record of the Gnostics sufferening persecution from the emperor).
But once Christianity became powerful enough, the emperor found a way to use the new religion to his advantage. Instead of declaring himself to be a god, he was now declared by the Church to be the ruler of the people. To the average Catholic in the Middle Ages, Jesus Christ appointed the first pope, Peter, and Peter would appoint his successor, and his successor would appoint the next successor, until we get to the current Pope, who would crown the emperor and kings to be rulers of the people. So to revolt against an emperor or a king would be to ultimately revolt against Jesus Christ. If at any point the chain of authority is broken the who thing falls apart. If Jesus Christ was not God, then the emperor has no justification for his rule over the people. If the Pope was not ordained by Christ, then the Pope's crowning of the emperor is meaningless. And if the emperor is not the justifiable ruler, then who is? Who determines it? How do you determine it? Remember, the idea of electing your leaders was still hundreds of years later. No one even thought of that back then. If the emperor and the kings are not divinely ordained by God to be their rulers, then all you have left is anarchy.
So back then religious belief was wedded to politics. Even in pagan Rome, religious belief was important to maintain social order. Until the modern notion of separation of church and state was developed, religion had poltical implications. For example, after the Reformation, a British Catholic would see Mary as the legitimate queen. A British Protestant would see Elizabeth as the legitmate queen. Mary wanted all of England to be Catholic, and Elizabeth wanted all to be Protestant (even though privately Elizabeth was keeping many Catholic practices). What religion you believed would effect who you would have as your ruler.
Before our modern era, any religious view that opposed the prevalent religious view would bring anarchy. This is why the emperors and the kings violently opposed the Albigensians. It is no different than how we would react if Communists tried to take over our government. Today, we fight wars over poltical ideology apart from religion. We went to Viet Nam to fight Communism. In the Middle Ages, men would join the Crusades to fight the Albigensians, who threatened their religious and political way of life.