Heterodox

heterodox \HET-uh-ruh-doks\, adjective:
1. Contrary to or differing from some acknowledged standard, especially in church doctrine or dogma; unorthodox.
2. Holding unorthodox opinions or doctrines.

They fight with members of other faiths, who seem to challenge their claim to a monopoly of absolute truth; they also persecute their co-religionists for interpreting a tradition differently or for holding heterodox beliefs.
-- Karen Armstrong, Islam: A Short History