so...Islam is to blame for the instability in France and such areas?
Umm... not what I was saying. The original poster asked what the religious effects of no Islam might have been. I think that there is a good chance the lack of Islam would have led to stronger Western Mediterranean civilization and weaker Papacy - such situation could have also prevented the destruction of most of what was left by unstable, martial-oriented "classic-feudalistic" cultures to the north.
I'm sure the Copts didn't need the Inquisition to feel persecuted by the Byzantines....or for the Jews to feel slammed-into-a-wall by just about everyone.
As the Coptic rebellions of the late VIIIth and IXth centuries show with distinct clarity, their lot in Muslim Egypt was far from enviable. After that time, they were effectively too powerless to do anything.
The Inquisition was, by the way, an example, not a source of all evils in the world.
I say "states" because it's easier than saying "social and-or economic and-or linguistic zones that may or may not have rulers in common"
...and because I know I always forget things to put in all-inclusive definitions like that.
With the Byzantine presence in Italy not thoroughly compromised by the affairs elsewhere, reunification of Italy under a single power is possible - however (and in this I go back to Renaissanse Italian authors and their observations) the presence of independent Papacy always created a door for any would-be Christian invader (especially after Charlemagne's coronation), and always created unstable political structures. My point is that if the Byzantines were capable to concentrate their entire focus on Italy (and they definitely would have had the resources to do so if these resources were not tied up fighting the Arabs - not to mention they would have been quite willing to retake Italy too, given a chance), they would have ended up with a single polity there, which would have had much easier chance protecting the peninsula against the incursions. As it was in OTL, there were numerous smaller states and powerful (but not sufficiently powerful) Papacy that often used outside forces to accomplish their ends. That alone creates pretext for numerous invasions, especially when you consider that an average Papal reign is not that long, and different independent policies of the Holy See tended to lead to even more foreign interference at the behest of the current occupant or his enemies.