As I understand it, the Pope responded to pleas from the Eastern Empire to help them defend against the "expansion" of Islam. As far as I can tell (and I'm no expert), if it hadn't been for the Crusades, we certainly wouldn't be fighting the WOT now -- because we'd all already be Muslim (those of us whose ancestors survived the "expansion," anyway).
One point I will make: The Pope didn't have fraternal feelings toward the Eastern Empire... One of the many reasons (and there is a list) that he (and it just wasn't one Pope since the Crusades lasted over 200 years) fought was to reconcile the two warring factions of the Church by establishing strong Roman influences in the Greek territories and cause the Roman Church to become the dominant church in the region.
The Crusades were an invasion... not launched at the whole Islam Empire, but against the Holy Land only (to recover the holy relics from the hands of the infidel). This alone would be why I would disagree with your post.
Of course, these two paragraphs are very shallow in regards to history and motivation. Maybe we could discuss it further tomorrow.