Intolerance does seem out of place in religion and Karen Armstrong has written about it better than I can. My understanding of Islam begins with the call to approach each other from our sameness. As the same we can see qualities and learn to forgive mistakes. We aren’t so hard on each other then. With difference someone instantly becomes “not us” and though difference in an intellectual way is exciting and trains us to be tolerant and expansive, those are a lot of things to take into account in a moment of encounter so we simply recoil, note differences and dwell on that.
There appears in all belief system an “accepted” understanding of god. In Christianity each sect has a list in order to guide its members to performance of proper duty–group rules I guess. Growing up as a Unitarian I sensed that being good to people, thought clearly written in Biblical scripture was expected of me without further conditions or expectations. Other Christians were all over the map on following this rule and it confused me. In some ways I guess I was being too rigid? Sometime you believe something and can’t allow yourself excuses. Is that a form of intolerance?