Religion doesn’t “cause” bigotry and strife directly, as if it were a force of nature, but it excuses those things. It offers justification for extreme fundamentalism. The stories and lessons in most holy books confer a feeling of superiority and aloofness to their readers. Religious beliefs encourage thinking only a select few can posses “absolute truth” and that you, yes you, get to be one of the lucky ones. 
Bigotry would be difficult to practice in a world where everyone accepted the inherent equality of all people, where we all saw each other as equal human beings. By creating divisions between people, by emphasizing differences instead of emphasizing similarities, religious beliefs provide fuel to the bigots fire. Religious self-righteousness is the gasoline poured on the flames.
