Well religion is just a small part of the dangers of group thinking. When people chose to be or believe something the opposite automatically becomes the enemy of that choice. You see it in racism, hatreds for other cultures and religions, clothing styles, types of music ect ect.
The truth is people fear change and people who manipulate religions feed the fear that the others are out to destroy their way of life. Most religions teach peace just all leaders are corrupt and use it for their own means. If you got ride of religions people just fight over what color is better or type of music and what not.