Since the collapse of the Western Empire, the West had descended in the eyes of the East to utter barbarism
They stopped speaking the same language -- Latin was not understood in the 11th century in the East and very few in the West understood Greek, indeed the literacy levels in the West were abysmal compared to the East
Culturally and politically they were also quite distinct
The Venetians were the cause of the 4th C tragedy -- they were, until the 10th century a part of the Byzantine Empire and shrugged it off while keeping their trading ties
in time they became an economic rival to the Byzantines, keeping troops and colonies in Byzantine areas
The Byzantines, government and people, didn't like this and it lead to the "slaughter of the Latins" 10 years before the 4th C
Venice waited for its revenge -- it could not stand up to the Byzantines militarily, so it diverted the attention of the Germanic 4th crusaders to Byzantium
The Byzantines were appalled at the sight of the dirty, barbaric hordes from the west. Perhaps some of them compared these to the Caliphate who were Romanized and well, cleaner and wondered if it was worth it
Anyway, the westerners felt they were not treated well -- they were probably expecting to be treated as saviors, while they weren't treated that way and it took little for the Venetians to divert their attention and to sack Constantinople
This was among the most shameful of Christian on Christian acts and one for which I (who normally think apologizing for centuries past events is silly) fully agree with Pope JP II who begged for forgiveness for this.
As Christians we have shamefully not stood together and have fallen to the common enemy -- the 4th C and then in the Crimean War when Anglican England and Catholic France fought on the side of the Moslem Turks against our Christian brethren and in the 1683 siege of Vienna when Calvinist Hungarians fought on the side of Moslem Turks against Catholic Hungarians, Austrians, Poles-Lithuanians-Ruthenians, Croats etc. (just as a historical note -- the Moslem Tartars fighting in the Polish-Lithuanian commonwealth army were very loyal in the fight against the Turks even though they even shared a similar language - Turkic)
What you were describing could be said that when Blessed JPII asked for the forgiveness of the Eastern Orthodox Christians for what took place during the time of the crusades, the sacking of Constantinople, what took place back then was the “worse” example of when Christian brother fought against Christian brother.