[Antoninus]

I have a Greek Orthodox friend who has nothing good to say about the Crusaders and their motives.

Of course not. The Crusaders were, by-and-large, ill-used by the Byzantine Emperors. They were treated like barbarian mercenaries who were to do the Emperor's bidding and not expect anything in return. Both sides viewed each other as potential back-stabbers. Promises were broken by both sides. By 1200, they were openly at swords' points with each other.

The truth is, as with any large mass movement, some Crusaders were in it for noble reasons (win back the Christian Levant, make the place safe for pilgrims, halt the Islamic advance), others for more base reasons (personal wealth, acquisition of kingdoms). As for the Byzantines, they too had mixed motives. They had been asking for Western help against Islam and when they got it, they immediately realized how dangerous it was to their own precarious position. This led to double-dealing, refusal of assistance, and barely suppressed relief when Crusader armies were annihilated in Asia Minor.

[nuke rocketeer]

And they got paid back by the crusade that sacked Constantinople at the urging of the Venetians. This probably took 100 years off the life of the Eastern Empire.