Because it was not just an attack by individuals, but a concerted attempt to wipe-out Orthodoxy.
There was established a Latin seat in Constantinople, and Latins then went out and forced conversions upon Orthodox. Perhaps you wish this instead to be an example of the powerlessness of the Pope?
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I have spoken in various threads about the insoucience the West has too often shown toward Orthodoxy. But we need to get this straight. There was plenty of blame to go around in the Fourth Crusade. The Crusaders wanted to enter Palestine by way of Egypt, but were dependant on Venice for transport. Venice had, however, made a deal with Egypt to divert the Crusaders. The Byzantine Emperor Manuel enraged Venice by arresting thousands of its merchants, thus assuring himself of a powerful enemy. His successor, Isaac Angelus, was deposed by his brother, who imprisoned and blnded him. Isaac’s son, Alexius, went to Europe and persuaded the Crusaders that if they would restore Isaac (and him), he would pay a large sum to pay for the crusade, provide 10,000 men to help the Crusaders in Palestine, and return the Orthodox Church to union with Rome. Pope Innocent III, hearing of this, threatened excommunication on any Crusader who attacked Byzantium. Nevertheless, the Crusaders did not have the price of transport and agreed to go to Byzantium. On arrival, they insisted on restoration of Isaac and his son, which the Greeks did. However, when the Greeks learned of the price in money, they revolted, killed Alexius, re-imprisoned Isaac, refused to pay the Crusaders what Alexius had promised and raised an army to attack the Crusader camp outside the city. Learning of this, the Crusaders laid siege to the city, took it and looted it, adding insult to injury by placing a Crusader on the throne. Shortly thereafter, the crusade fell apart.
The biggest villains in the piece were probably the Venetian Doge, Dandolo, and Alexius. But there was poor judgment and immoral action all around. The Greeks should have known it was unwise, at minimum, to renege on Alexius’ promise, since the Crusaders had no place to go without the cost of transport. They should have known they could not resist the Crusader army. The Crusaders defied the Pope and let their purpose be diverted by Byzantine gold after the walls of the city were breached.
But it was no massacre. Some 2000 Greeks died in the ordeal, which was not unusual in the siege and conquest of a city of that size. It did not result in the Turkish conquest. At no point were there more than 4500 knights and 20,000 infantry int he Crusader army. The Turkish conquest did not take place until two centuries later, and the Turkish army was 140,000 men. Internal weakness, not the Crusaders, were responsible for the city’s fall. There were no forced conversions. A delegation of Latin and Orthodox clergy offered reunion to Rome, which was accepted, thus rendering conversion moot. No doubt many Orthodox resented it, and might have been right in resenting Alexius’ deal and the offer of reunion. But it was not a forced conversion.
Nor were the Greeks all that clean. They refused to aid the Serbs at Kosovo, as well as other Orthodox, against the Turks. More than once they sent Byzantine troops to aid the Turks against Orthodox in the Balkans. Even so, the West ought to have aided them, notwithstanding that other Orthodox peoples also refused to help them when their need came.
Before, during and after the Fourth Crusade, Pope Innocent III condemned it, and that should be admitted.
Pope John Paul II apologized to Orthodoxy for Latin misdeeds, including those of the Fourth Crusade. Pope Benedict has extended his hand to Orthodoxy. The real threats to Latin and Orthodox Christianity are Islam and secularism, not each other. It is time to stop focusing on old injuries and to get serious about rapprochement.
This is not an ‘excuse’ but perhaps you’ve fallen for the idea that the Crusades were the beginning of this aggression.