Is religion the most polarizing force on the planet? Why do you think that is?

Plenty of examples on Y/A show that nothing can make a person angrier or more resolved than religious beliefs. Why can't devout religious believers accept non-believers for who they are? Why can't atheists let religious believers shout what they believe as loud as they want? I'm not sitting on the fence, as a liberal Catholic, my faith is personal and not something to share with others. I hope tolerance prevails someday...