Why do people feel the need to identify with a religious group?

Isn't the concept of most religions the same? Creator, afterlife, God, etc. To me all of them tell a very similar story. Why get in these extremist groups and cults and bully each other in the name of God? You'd think after thousands of years petty bickering over who's right would get old. So, why do you choose to identify with a certain religion?