This is extremely odd history. Slanted to the point of being totally one-sided. Here are some additional points that give balance.
In the events of the middle 1000’s, the Patriarch was the odd man out. He was hostile to the Emperor and eventually was sent packing, sadly not soon enough.
The Pope and Emperor were like minded in resisting the Normans, but were defeated. The proximate cause of the the dispatch of Humbertus was the grotesque desecration of the Blessed Sacrament, supported by Cerularius, over that giant issue, azymes, which carried over from Byzantine polemics against the Armenians - and vice versa.
Were there clear canonical reasons and processes for closing the Latin churches, or was this just political maneuvering as with the azyme issue?
The bull of excommunication has been very cutely translated to make Humbertus look foolish, but that also is largely polemics.
The Emperor received the Cardinal graciously - again the Patriarch was the odd man out.
Is there any foundation for the idea that the Emperor knew that the legates were acting without authority after the death of the pope who dispatched them? If so, why the nuclear response to a paper tiger? A response that was not respected by the other Eastern Patriarchates that were controlled by the EP.
As to the Crusades:
After Manizikert it was all over for Byzantines, unless they could get help and recover Anatolia.
The crusaders were invited and put their lives and fortunes on the line to support the Byzantines, but were treated with duplicity and treachery by them - not only by the stridently anti-western faction that held control from time to time, but in general: the Byzantines were always playing both sides.
The installation of a Latin Patriarch into a vacant see in Jerusalem was not irregular given Latin control of the region, the common role of the civil authorities in authorizing episcopal appointments in the East, and the large influx of Latin clergy. The situation in Antioch was different, but then again, not much can be said to canonically support, the subsequent of appointment by the EP of Greeks, resident in Constantinople as Antiochian Patriarchs - an irregularity that prevailed until recent times, and was a factor in the lawful reunion of the church of Antioch with Rome in the 1700’s.
In the fourth Crusade, the Crusaders were invited into Constantinople by a claimant to the Emperor’s throne, who promised support for the campaign to Egypt. The Pope had already excommunicated the group after they sacked a Latin town for Venice to get the financial support for the mission. The campaign was successful, but the payoff was not received - the anti-western faction (recently behind the massacre of many thousands of Westerners, including women and children) murdered the new emperor and reneged on the deal. The Crusaders collected. War is hell. Too bad that they didn’t resume the campaign, but it’s not hard to see why they thought it a good idea to stay.
Again, these points are added for some balance. The one-sided view of Orthodox history seems to recount every sin against the East as though it happened yesterday, but rarely (DB Hart, a notable exception) seems to give a sober account of its own culpability.
What Fr Taft says.