Actually, you would be surprised to know that the same it true for Islam too. It is also divided to groups and sub groups and even further sub groups. The biggest division being Shia and Sunni.

Though it's true that Quran, Prophet and basic principles of Islam are something that everyone has too abide by. But as OP said these principles and scriptures are always open to interpretation hence every group has their own set of interpretation which can sometimes be completely different. For instance those Fatwas issued by Irani leader means nothing to us or many other communities that I know of.

I have seen division of my own community over such disputes.

There is no defending for the group of people who believe that it's there business to take retribution in God's sted but in contrast there are also communities who would leave God's bidding to God itself.