Belief or idea?

Man, was it because it was Super Bowl Sunday that the networks decided to show stupid programs all day? The weekends that are mine (which are few and far between), I can leave the channel set to one for most of the day. Yesterday I had flipped through my channels a couple times before I left for the gem show.

Same when I came back. However, Comedy Central did show "Dogma". The scene I came in was the one where Bethany was on the train talking with Rufus on the train. Rufus says something that makes a lot of sense to me:

"It's better to have ideas instead of beliefs. You can change an idea...people die for beliefs."

Seeing the backlash to several European countries by angry Muslims make me think about this from Dogma. People fight for their beliefs, people die for their beliefs. When it comes to religion, it seems to me that since there's more than one major religion and they share some of the same elements, maybe it's better to have ideas instead of beliefs.

Will someone explain to me how Christinanity and Judiasm became so distinct from one another when they started from the same book?