you could use an analogy here using different Christian sects/denominations. They don't see eye to eye on exactly how the bible is to be interpreted. Yet, do they not unite on several issues even though there are "deep internal divisions"?
True, but the difference here is the devout followers of the various Christian sects aren't killing each other over the interpretation of Bible passages and killing isn't seen as an act worthy of an eternal reward. Quite the opposite. I also think that Christians tend to be more modern and open to Capitalism, thus have the notion of bettering themselves and futures of their children. I don't see a lot of that in the Muslim world. Can you imagine a Presbyterian teaching his kid to be a suicide bomber? I can't.