The answer is: Fundamentalism usually has a religious connotation that indicates unwavering attachment to a set of irreducible beliefs.
In religious community, fundamentalist people tend to be more inclined to interpret the bible through the literal translation of the text. If being done in a extreme level, this could lead to a close mindedness, and often create a situation where that people feel that they had the moral high ground to judge others and force them to conform to their interpretation.