they had to be pretty passionate about the "petty differences". In many cases lives were threatened or taken.
Sadly, that is true. However, the passionate ones who create the atmospheres the take lives are often the leaders, or those who aspired to become the leaders. The majority of followers, then as now, were and are just that: followers eagerly doing as they are taught. The passionate ones who incite the zealous fervor are relatively few. It took being away from all religion for many years, followed by marriage to a Witness woman, before I realized how just much the various factions actually have in common.
Many religions do not follow Jesus.. I would say these are major differences. That is the foundation of Christianity, Jesus.
Case #1, Jesus: Granted, my comments were primarily centered on Christianity. Christians accept Jesus as fullfillment of Old Testament prophecy, Jews do not. But both Christians and Jews accept the Old Testament that contains those prophecies.
Case #2: Christians, Jews and Moslems all believe in the God of Abraham, though in different ways and by different names.
Even comparing to religions that didn't originate in the middle East, there is similarity.
Case #3, reincarnation: Christians believe in a second life, while disagreeing on whether it is spiritual, physical, or some blend of the two. Hindus also believe in reincarnation, physical reincarnation, until perfection is attained allowing one to join the divine. Christians share the belief that "self" is not limited to our present physical body, that there is a soul, a future life and reunion with God. Buddhism teaches a more figurative rebirth rather than a literal one, but shares the concept of attaining an ideal state, nirvana. Yes, the details and names differ considerably; but the basic premise is similar.
Case #4, right and wrong: The standards for conduct have much in common: you may not murder, lie, steal, or act immorally. You are expected to treat other persons fairly, and expect them to do the same to you. This is the concept of natural law.
Yes, I do think there is considerable agreement on the moral and spiritual levels. These are what I consider to be the important similarities. The differences are not so great until aggravated by man-made passions. That polarized "I'm completely right so you must be completely wrong!" attitude is what I am calling a false dichotomy. As Palimpset said, some faiths do take this to heart.